Automotive Glossary

Automotive Glossary

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The common descriptive title for paints that require the addition of a hardener (without which they will not cure).
Entry link: 2K



Anti-lock braking system.
Entry link: A.B.S


American Petroleum Institute.
Entry link: A.P.I.

A.P.I. (C)

American Petroleum Institute classification for oils suitable for diesel (compression ignition engines).
Entry link: A.P.I. (C)

A.P.I. (S)

American Petroleum Institute classification for oils suitable for gasoline (spark ignition) engines.
Entry link: A.P.I. (S)


Engine lubricating oil classification suitable for basic petrol and diesel engines.
Entry link: A.P.I. SC/CC


Engine lubricating oil classification suitable for modern engines.
Entry link: A.P.I. SG/CD


Air Conditioning
Entry link: A/C

A/C - Air Conditioning

Air conditioning system that uses a refrigerant to remove heat from the air entering the passenger compartment.
Entry link: A/C - Air Conditioning

A/D Converter

An electronic device used to convert analog values to digital signals for electronic control units and instruments.
Entry link: A/D Converter


Air/Fuel Ratio
Entry link: A/F


Automatic transmission.
Entry link: A/T


The term used when a test cannot be completed because the NT considers it unsafe to continue or because it becomes apparent during the test that certain items cannot be satisfactorily inspected. An appropriate fee may be charged for the test.

Entry link: Abandon


The term used when a test cannot be completed because of a problem with the VTS’s/DC’s testing equipment or the NT. No fee may be charged for the test.

Entry link: Abort


Wearing away of a surface by some external force, such as sanding.
Entry link: Abrasion


Substance used to wear away or smooth a surface by friction.
Entry link: Abrasive


Substances used to wear away a surface by friction.
Entry link: Abrasives


Antilock braking system.
Entry link: ABS

Absolute Pressure

The pressure that exists when the forces of gravity are excluded from the actual pressure. Absolute pressure is equal to gauge pressure plus atmospheric pressure.
Entry link: Absolute Pressure


The penetration of a solid substance by a liquid as by capillary, osmotic, solvent, or chemical action.
Entry link: Absorb


Of heat: Takes in heat energy. Of sound: Takes in sound energy.
Entry link: Absorption


Air Bypass Solenoid Valve
Entry link: ABSV


Alternating Current
Entry link: AC

AC - Alternating Current

An electrical current that flows in forward and reverse bias alternately.
Entry link: AC - Alternating Current


To speed up a process.
Entry link: Accelerate


Increasing velocity or speed.
Entry link: Acceleration


A substance that, when added to a paint, will speed up the rate of cure.
Entry link: Accelerator

Accelerator Pump

Carburettor pumping system that introduces flow of fuel into the carburettor choke (venturi) on acceleration, particularly when accelerating from low speeds.
Entry link: Accelerator Pump


A hydraulic device that dampens the pulses and retains a residual pressure in a hydraulic circuit.
Entry link: Accumulator


How close the data given is to the true value.
Entry link: Accuracy


Association des Constructeurs Europeens d'Automobiles. The European organisation that sets specifications for lubricants. There are three categories for engine oils. A for gasoline/petrol engines. B for light vehicle diesel engines. C for commercial vehicle diesel engines.
Entry link: ACEA


A very fast evaporating solvent with high solvency for certain types of compounds and resins. Has a characteristic ether-like odour.
Entry link: Acetone


An inorganic or organic compound that (1) reacts with metals to yield hydrogen; (2) reacts with a base to form a salt. They are corrosive to human tissue and should be handled with care. Examples are hydrochloric acid, sulphuric acid, and nitric acid.
Entry link: Acid

Acid Rain

Forms when pollution is combined with water in the atmosphere. When sulphur dioxide and nitrogen oxides mix with water molecules, they form weak sulphuric and nitric acids. As the water evaporates, the acids gain strength and can etch the finish of any vehicle upon which they have been deposited.
Entry link: Acid Rain

Acidic Compounds

Harmful chemicals that are formed during combustion and can contaminate engine oil. Sulphur in fuel can form sulphuric acid which can cause corrosion, sludging and lubricating oil defects.
Entry link: Acidic Compounds

Ackerman Principle

System of steering that produces wheel turning axes around a common point.
Entry link: Ackerman Principle


A coating based on a polymer containing short chain esters of acrylic and methacrylic acid. One-pack Acrylics were once widely used as automotive topcoats, but have generally been replaced by water-borne base colours overcoated with two-pack Acrylic clear coats
Entry link: Acrylic

Acrylic Urethane

A coating based on urethane chemistry which also includes acrylic chemistry as part of the cross-linked polymer backbone.
Entry link: Acrylic Urethane


Air conditioning switch.
Entry link: ACS

ACT - Air Charge Temperature

Air charge temperature sensor measures the intake air temperature on fuel injection systems.
Entry link: ACT - Air Charge Temperature


A necessary component used to provide a chemical reaction to cure paints, resins and adhesives.
Entry link: Activator


A system that takes action all the time as opposed to a passive system that waits for a specific event before reacting.
Entry link: Active


Air Charge Temperature Sensor
Entry link: ACTS


Electronic components that receive signals from an electronic control unit (ECU) and operate to make a system work.
Entry link: Actuators


General term used to describe a device that allows one component to fit with another.
Entry link: Adapter

Adaptive Memory

A computer memory process that allows for changes in an open-loop mode.
Entry link: Adaptive Memory


A chemical added to improve the properties or performance of something.
Entry link: Additive


Chemical substances added to paint products in relatively small amounts to impart or improve desirable properties. Examples include UV screeners, flow agents, and fish eye eliminators.
Entry link: Additives


The phenomenon by which one material is attached to another by means of surface attraction.
Entry link: Adhesion


General term used to describe a component that changes the adjustment of something (brake shoes or brake bands for example).
Entry link: Adjuster


Guidance offered by someone.
Entry link: Advice


Authorised Examiner – the organisation that operates and manages one or more VTSs and is responsible for controlling the quality of testing carried out. Except in the case of a ‘sole trader’ the AE is not a person but a legal entity (e.g. a company or partnership).

Entry link: AE


Air mixture in a hydraulic liquid that reduces the performance of a hydraulic system.
Entry link: Aeration

Aesthetic Value

A value put on how nice or appealing something looks.
Entry link: Aesthetic Value


Air Flow Control
Entry link: AFC


Air Flow Meter
Entry link: AFM


Air Flow Sensor
Entry link: AFS


Clumps of pigment particles which have formed loose clusters. Usually undesirable in paint, since agglomerates tend to settle out and exhibit poor colour or 'seeds', which are small granular deposits, other than dust, found in paint, varnish or lacquer colour.
Entry link: Agglomerate


A paint stirrer.
Entry link: Agitator

Agitator Cup

Paint cup used with high metallics and pearls to keep the pigment particles in suspension by continually mixing the paint. This ensures better colour uniformity.
Entry link: Agitator Cup

Air Bleed Valve

An automatic device used on fuel injection systems to provide fast idle during cold start and warm up.
Entry link: Air Bleed Valve

Air Cap

Fitted in front of a spray gun fluid nozzle to direct compressed air against the paint to form and shape an atomised cloud of droplets.
Entry link: Air Cap

Air Charge

Description of the amount of air taken into an engine on the induction stroke.
Entry link: Air Charge

Air Cleaners/Filters

Canisters holding paper, plastic foam or gauze elements to trap dirt and grit.
Entry link: Air Cleaners/Filters

Air Dry

The ability of a coating to dry or cure to its ultimate hardness under normal atmospheric conditions, without baking or force-drying. Measurement of time required must state conditions such as temperature and humidity.
Entry link: Air Dry

Air Flow

Movement of a quantity of air past a point in a set time.
Entry link: Air Flow

Air Flow Meter

Provides information to fuel injection system electronic control unit (ECU) on engine load. Measures the mass of air entering an engine.
Entry link: Air Flow Meter

Air Flow Sensor Plate

A plate used to sense the movement of air and therefore control fuel quantity.
Entry link: Air Flow Sensor Plate

Air Gap

The gap between two parts of a component, such as the spark plug electrodes, an inductive sensor or an armature and field shoes of a motor or generator.
Entry link: Air Gap

Air Horn

The air inlet side of a carburettor or throttle body assembly.
Entry link: Air Horn

Air Injection

An emission control device that adds air to the exhaust to add oxygen for the conversion of hydrocarbons and carbon monoxide to water and carbon dioxide. Usually fitted upstream of a catalytic converter.
Entry link: Air Injection

Air Intake Duct

A pipe or similar used as part of the intake manifold or general system.
Entry link: Air Intake Duct

Air Line

A pipe that delivers compressed air.
Entry link: Air Line

Air Lock

A bubble of air in a hydraulic system that can be compressed and therefore reduces the performance or causes failure of the system.
Entry link: Air Lock

Air Ratchet

A ratchet wrench driven by compressed air.
Entry link: Air Ratchet

Air Resistance

Friction force caused by, for example, a vehicle moving through the air.
Entry link: Air Resistance

Air Spray

A system of applying paint in the form of tiny droplets. The paint is broken into droplets (atomised) by a spray gun as a result of being forced into a high velocity air stream. The shape and paint density of the resulting droplet cloud can be controlled by variations in air pressure, paint viscosity and gun tip geometry.
Entry link: Air Spray

Air Temperature Sensor

Electronic device that provides information for engine management systems and frost warning indicator.
Entry link: Air Temperature Sensor

Air-fuel Ratio

The air and fuel mixture strength ratio.
Entry link: Air-fuel Ratio

Airflow Meter

Provides information to fuel injection system electronic control unit (ECU) on engine load. Measures the mass of air entering an engine.
Entry link: Airflow Meter

Airflow Sensor Plate

Mechanical fuel injection component that moves in proportion to the air intake and sets fuelling accordingly.
Entry link: Airflow Sensor Plate

Airless Spray

A system of applying paint in which the paint, under extremely high pressure, is passed through a nozzle and breaks up into droplets as it enters the lower pressure region outside the gun tip.
Entry link: Airless Spray


A pipe that delivers compressed air.
Entry link: Airline


Assembly Line Communications Link
Entry link: ALCL


Assembly line communication or diagnostic link. A multisocket connector for attaching a diagnostic tool to a vehicle electronic system.
Entry link: ALCL/ALDL

Alcoholics Anonymous

A worldwide group of men and women who meet in order to help one another stop drinking alcohol and remain sober.
Entry link: Alcoholics Anonymous


Assembly Line Data Link
Entry link: ALDL


Bringing into line.
Entry link: Alignment


A chemical 'base' (loosely, the opposite of an acid). Certain types of alkalis have been used as fuel cell electrolytes.
Entry link: Alkali


A coating based on a polyester binder. Such polyesters are chemical combinations of molecules that contain more than one acid or alcohol group.
Entry link: Alkyd


A name used to describe a hexagonal key.
Entry link: Allen


A mixture of metals and other elements to form a metal with specific properties such as phosphor bronze used for bushes.
Entry link: Alloy

Alternative fuel

A fuel used in vehicles that comes from a source other than petroleum, such as ethanol made from corn and biodiesel made from vegetable oil.
Entry link: Alternative fuel


An electrical generator attached to and driven by a motor vehicle engine.
Entry link: Alternator

Alternator Brushes

Soft carbon brushes that conduct electricity to the field windings via the slip rings.
Entry link: Alternator Brushes


Non-ferrous metal used as a substrate or a pigment.
Entry link: Aluminium

Aluminium Oxide

Sharp and hard abrasive - used in dry-flatting Production papers
Entry link: Aluminium Oxide

Ambient Pressure

Air pressure in the surrounding area.
Entry link: Ambient Pressure

Ambient Temperature

Temperature of the air surrounding an object.
Entry link: Ambient Temperature


Instrument for measuring electrical current.
Entry link: Ammeter


A compound of nitrogen and hydrogen with the formula NH3. It is normally encountered as a gas with a characteristic pungent odour but can be included in a water based form into cleaning compounds for example.
Entry link: Ammonia


Strength of an electrical current in amperes.
Entry link: Amperage

Ampere (Amp)

Electrical unit for measuring the flow of electricity in a circuit.
Entry link: Ampere (Amp)


Discharge rate used to describe what a battery will produce. For example, a 40Ah battery will produce 2A for 20Hrs. The 20hrs is an agreed value used to allow comparisons to be made.
Entry link: Ampere-hour-rate


An increased electrical voltage and/or current compared to say the original signal.
Entry link: Amplification


An electronic device that increases or allows an increased electrical voltage and/or current to flow.
Entry link: Amplifier


The maximum distance moved by a point on a vibrating body or wave measured from its equilibrium position. It is equal to one-half the length of the vibration path i.e. half the peak to peak value of a wave.
Entry link: Amplitude


Short for Ampere (unit of electrical current)
Entry link: Amps


Used to describe a sealant that dries when air or oxygen is excluded.
Entry link: Anaerobic


A measuring process that uses a variable electrical current to provide a signal for computers and instruments.
Entry link: Analog

Analog Gauge

An instrument readout that displays using a moving needle or similar method.
Entry link: Analog Gauge


A measuring process that uses a variable electrical current to provide a signal for computers and instruments.
Entry link: Analogue

Analogue Gauge

An instrument readout that displays using a moving needle or similar method.
Entry link: Analogue Gauge

Anionic Electrodeposition

One of the electro-coating methods in which the body is charged positively and completely immersed in the negatively charged paint. Frequently used for OEM primer application, the resultant coating is known as 'E-coat'
Entry link: Anionic Electrodeposition

Annual Income

Amount of money you earn each year.
Entry link: Annual Income


The outer gear with internal teeth on an epicyclic gear train.
Entry link: Annulus


A positive connection.
Entry link: Anode

Anodised Aluminium

A surface treatment for aluminium that adds an oxidised coating to harden the surface of the component.
Entry link: Anodised Aluminium


An electrolytic surface treatment for aluminium which builds up an aluminium oxide coating, to provide better adhesion.
Entry link: Anodising


Protective coating applied on metal surfaces to prevent corrosion.
Entry link: Anti-corrosive


A chemical such as ethylene glycol, added to the cooling water of an engine to lower the freezing point for winter operation.
Entry link: Anti-freeze


Usually used to refer to an additive that is added to fuel, which makes the burning process more controllable, resulting in reduced tendency to knock.
Entry link: Anti-knock

Anti-roll Bars

Suspension component that reduces vehicle roll.
Entry link: Anti-roll Bars

Anti-skinning Agents

Chemicals added to a paint to help prevent the formation of a surface film during storage.
Entry link: Anti-skinning Agents

Anti-trap Function

Facility to prevent electric windows closing and trapping something - your fingers for example! See also Bounce Back.
Entry link: Anti-trap Function


Additive put in the cooling system to prevent freezing.
Entry link: Antifreeze


A metal, which is added to lead, to improve its mechanical strength. Batteries were traditionally constructed with lead-antimony.
Entry link: Antimony

Antivirus Software

A software package that prevents computer viruses from damaging or destroying the system.
Entry link: Antivirus Software


Another name for a computer program such as Microsoft Word.
Entry link: Application

Applied Solids

Solids that remain on the substrate being coated or painted.
Entry link: Applied Solids


Absolute Pressure Sensor
Entry link: APS

APS - Absolute Pressure Sensor

A barometric pressure sensor used to compare atmospheric and manifold pressures in electric fuel injection systems.
Entry link: APS - Absolute Pressure Sensor


The effect when a vehicle's tyres tend to skid on top of water on the road.
Entry link: Aquaplaning


Describes a water-based solution or suspension (see 'waterborne').
Entry link: Aqueous


Conduction of electricity across a gap. An arc is caused as contacts open.
Entry link: Arcing


Length x width
Entry link: Area


Electrical windings around the core fixed to the spindle of a motor or dynamo.
Entry link: Armature


The smell of something such as perfume or worse...
Entry link: Aroma


A type of solvent based on benzene ring molecules.
Entry link: Aromatics


Fibrous silicate material that can be woven into an incombustible fabric. Requires special handling as it is a hazardous substance.
Entry link: Asbestos


Airbag System Diagnostic Module
Entry link: ASDM

Aspect Ratio

Ratio of two axes at right angles to each other such as the long and short sides of a rectangle. When applied to low profile tyres it refers to the width and depth and is shown as a percentage value in the tyre size marking.
Entry link: Aspect Ratio


Breathing or induction process of an engine. Non-turbocharged engines may be described as naturally aspirated.
Entry link: Aspiration


The teacher or tutor, who assesses the portfolio of evidence.
Entry link: Assessor


A description of objects that are different on each side of their centre line.
Entry link: Asymmetrical


After Top Dead Centre
Entry link: ATDC

ATDC - After Top Dead Center

ATDC - Before Top Dead Centre.
Entry link: ATDC - After Top Dead Center

ATDC - After Top Dead Centre

The position of the crankshaft when the piston has passed the top of the cylinder and is on the way down.
Entry link: ATDC - After Top Dead Centre


Automatic Transmission Fluid.
Entry link: ATF


Automated Test Lane – These are lanes authorised by VOSA of use in the automated mode.

Entry link: ATL


The air that surrounds the Earth's surface.
Entry link: Atmosphere

Atmospheric Pressure

Pressure in the atmosphere produced as a result of the Earth's gravity. Measured at sea level it has a value of 1 Bar, 14.7 psi or 100 kPa.
Entry link: Atmospheric Pressure


Smallest particle in a chemical element that can take part in a chemical reaction. A single particle of an element.
Entry link: Atom


Relating to the atom...
Entry link: Atomic

Atomic clock

This is a type of clock that uses an atomic resonance frequency standard as its timekeeping element. It is very accurate.
Entry link: Atomic clock


The formation of tiny droplets of liquid as in the paint spraying process. Atomisation is usually achieved by turbulence in an air stream, or a sudden drop in pressure.
Entry link: Atomisation


The stage in which the metered air/fuel emulsion is drawn in to the airstream in the form of tiny droplets.
Entry link: Atomised


Breaking up of fuel into fine particles during induction into an engine.
Entry link: Atomization


The stage in which the metered air/fuel emulsion is drawn in to the airstream in the form of tiny droplets.
Entry link: Atomized


Air Temperature Sensor
Entry link: ATS


Of or relating to the ear or to the sense of hearing - aural diagnostics mean listening for faults such as a bearing noise or a misfire
Entry link: Aural


See Automatic Transmission
Entry link: Auto-box

Automatic Adjusters

Brake components that automatically take up wear to keep brake shoes or pads close to the drum or rotor.
Entry link: Automatic Adjusters

Automatic Choke

A carburettor component using a bimetallic strip that operates at low engine temperatures to improve cold start and idle performance. Operates independently of the driver.
Entry link: Automatic Choke

Automatic Transmission

A vehicle gearbox with automatic gear shifts based on engine speed and load conditions. Does not require individual gear shifts by the driver.
Entry link: Automatic Transmission

Auxiliary Air Flow

Used to describe a flow of air that bypasses the normal route. It is used to control idle speed or idle mixture.
Entry link: Auxiliary Air Flow

Auxiliary Air Valve

A valve used to control auxiliary air flow.
Entry link: Auxiliary Air Valve

Auxiliary Components

Components that are outside a specific system. For example, when working on the engine, an alternator would be described as auxiliary.
Entry link: Auxiliary Components

Auxiliary Lights

Extra, non-essential lights such as front spotlights or driving lights.
Entry link: Auxiliary Lights

Auxiliary shafts

Shafts that are used on some engines for balance or to drive other components.
Entry link: Auxiliary shafts

Avalanche Diode

A diode that conducts when a value voltage is applied. Used to protect circuits from overload.
Entry link: Avalanche Diode


The sum divided by the number of items.
Entry link: Average

Awarding body

There are several awarding bodies City and Guilds: AQA, Edexcel and OCR for example.
Entry link: Awarding body


Transmission system that uses all four wheels of a vehicle to provide a drive. This term is usually used on vehicles with a permanent four wheel drive that transfers drive to another axle when some loss of drive occurs on the main drive axle. The term 4WD or 4x4 is used for used for vehicles with selectable four wheel drive.
Entry link: AWD

AWD - All Wheel Drive

Transmission system that uses all four wheels of a vehicle to provide a drive. This term is usually used on vehicles with a permanent four wheel drive that transfers drive to another axle when some loss of drive occurs on the main drive axle. The term 4WD or 4x4 is used for vehicles with selectable four wheel drive.
Entry link: AWD - All Wheel Drive

Axial Loading

Along the axis of a shaft.
Entry link: Axial Loading

Axial Motion

Movement along or parallel to the axis of a shaft.
Entry link: Axial Motion


The centre line through a shaft or axle. The centre about which an object rotates or where the object is in equilibrium.
Entry link: Axis


Horizontal transverse shaft or beam with spindles on which road wheels are mounted.
Entry link: Axle

Axle Loading

Term used to describe the forces acting on an axle.
Entry link: Axle Loading

Axle Mounting

Method of fixing the axle to the body or springs.
Entry link: Axle Mounting

Axle Stands

Vehicle support equipment manufactured with a rated weight capacity. Used to support a vehicle when wheels are removed or when access to the underside is needed. Also known as jack stands.
Entry link: Axle Stands

Axle Windup

A condition in an axle where the driven component locks and the axle casing attempts to rotate on its mountings. Usually caused when a differential lock or limited slip device is used and wheel spin is not possible such as on a dry road.
Entry link: Axle Windup



Body CAN or Basic CAN
Entry link: B-CAN


British Association old standard size of threads."
Entry link: B.A

B.S. Kite Mark

British Standards Kite Mark. The symbol of the British Standards Institute consisting of a triangle on its point with a capital B on its side above the triangle and a capital S inside the triangle.
Entry link: B.S. Kite Mark


British Standard Fine size of thread."
Entry link: B.S.F


Battery Positive Voltage
Entry link: B+

Babbitt Metal

An alloy of tin, copper, antimony and lead used as a coating for plain steel bearings.
Entry link: Babbitt Metal

Back EMF

A voltage produced that tends to oppose the voltage that created it.
Entry link: Back EMF

Back Plate

(1) Non-rotating plate carrying the shoes of a drum brake. (2) Metal member carrying friction material of the disc brake pad.
Entry link: Back Plate

Back Pressure

The pressure build-up in the exhaust caused by the resistance to exhaust flow by pipe diameters and muffler baffles. Used in design to balance an exhaust to an engine.
Entry link: Back Pressure


Technique of sanding a surface to taper the paint film away from the metal repaired area.
Entry link: Back-Sanding


Combustion of fuel in the intake or exhaust resulting in a loud explosive noise.
Entry link: Backfire


The base material of flatting paper onto which abrasive grains are coated. For masking tape, the backing is the paper section without the adhesive.
Entry link: Backing

Backing Pad

A supporting pad for abrasive disc and/or polishing pads that is attached to a polishing mop or a DA sander. In the compounding, glazing or polishing operation, a foam or wool polishing or glazing pad is attached on top of the backup pad. In dry sanding operations an abrasive disc is attached to the face of the pad.
Entry link: Backing Pad


The clearance between two components, usually used to measure the running clearance of gear teeth.
Entry link: Backlash


A second copy of work in case the original is damaged or destroyed. Should be stored away from the computer.
Entry link: Backup


A part fitted behind the air cap in a spray gun to direct the air stream and reduce air turbulence.
Entry link: Baffle


Application of heat to cure and dry a coating. In automotive refinishing, baking is used to speed up the drying of air-drying finishes and is sometimes called force-drying. The metal temperature in refinish baking usually does not exceed 80°C (180°F).
Entry link: Baking

Balance Shaft

A rotating shaft geared to another shaft, usually the crankshaft that carries counterbalance weights to bring the shafts into harmonic balance.
Entry link: Balance Shaft

Balance Valve

A hydraulic device that controls the pressure in different parts of a hydraulic circuit. Used to balance front and rear brake actuation.
Entry link: Balance Valve

Balance Weights

Small weights used to balance a shaft or a wheel.
Entry link: Balance Weights


Additive used to balance colour formulae in proportion to size and pigment-to-binder ratio.
Entry link: Balancer

Balk Ring

A component of a synchromesh gear hub that provides a cone clutch and guidance of the outer hub to the gear dog teeth.
Entry link: Balk Ring

Ball Bearing

A bearing consisting of inner and outer tracks with a series of ball bearings in between. A single surface hardened steel ball.
Entry link: Ball Bearing

Ball Flange

Flexible exhaust connection.
Entry link: Ball Flange

Ball Joints

Joints that allow movement for suspension and steering.
Entry link: Ball Joints

Ball Pivot

A pivot that allows movement in several directions.
Entry link: Ball Pivot

Ball Valve

A simple valve that is closed off as a ball moves.
Entry link: Ball Valve

Ballast Resistor

Electrical resistor used in low tension circuit to regulate ignition coil output when the engine is running and is by-passed during starting to give an increased spark voltage for cold starting.
Entry link: Ballast Resistor


The maximum amount of information (bits/second) that can be transmitted along a channel.
Entry link: Bandwidth

Banjo Joint

A hydraulic joint consisting of a hollow through bolt and a hose connector that looks like a banjo and from which it gets its name.
Entry link: Banjo Joint


Measurement of pressure - one atmosphere.
Entry link: Bar


Barometric Pressure
Entry link: BARO

BARO (Barometric Pressure)

Air or gas pressure measured in a standard unit. (Pascal, psi, bar)
Entry link: BARO (Barometric Pressure)

Barrier Cream

Used to help prevent skin damage when working, for example, with oils.
Entry link: Barrier Cream


Terminal of a transistor that becomes conductive to the emitter when energised. The trigger terminal of transistors and thyristors.
Entry link: Base


A colour coat requiring final protection in the form of a sprayed clearcoat. The basecoat provides colour effects and appearance, while the clearcoat provides gloss as well as UV and chemical resistance.
Entry link: Basecoat

Basic skills

Reading, writing, speaking in English (or Welsh) and using numbers sufficiently well to be able to function in society and at work. Key skills and basic skills overlap at levels 1 and 2.
Entry link: Basic skills


Entry link: BAT

Bath tub

An old type of combustion chamber looking like a bath tub when the cylinder head is turned over.
Entry link: Bath tub


A chemical device that will give out an electrical current when connected into a circuit.
Entry link: Battery

Battery Carrier

A tray to hold the battery, usually under the bonnet.
Entry link: Battery Carrier

Battery Grease

Petroleum jelly used on battery terminals.
Entry link: Battery Grease

Battery module

A generic term meaning a collection of battery cells and control systems. Often relates to EVs or HEVs.
Entry link: Battery module

Battery Posts

The main connections on a battery.
Entry link: Battery Posts

Battery terminal

See Battery Post
Entry link: Battery terminal

Battery Volts

A term used to describe the voltage of the particular system. This is often 12V - but could be 14V when the engine is running.
Entry link: Battery Volts


Body Control Module
Entry link: BCM


Bottom dead centre. The position of the crankshaft when the piston is at its lowest position in the cylinder. The crankshaft is at 180° of rotation from the top dead centre 0° position.
Entry link: BDC


Part of the tyre.
Entry link: Bead

Beam Axle

Type of non-independent suspension.
Entry link: Beam Axle

Beam Setter

Equipment used to check the alignment of vehicle headlights.
Entry link: Beam Setter

Bearing Cap

Half-round parts that holds the big end and main bearings into place either on the con rods or engine block.
Entry link: Bearing Cap

Bearing Clearance

The freeplay between a bearing shell and journal.
Entry link: Bearing Clearance

Bearing Nip or Crush

Applies to the applied grip of a split shell bearing when the two halves are tightened together.
Entry link: Bearing Nip or Crush


Components used to support a shaft and allow rotation.
Entry link: Bearings

Bell Housing

Cover over the clutch assembly. Usually joins the gearbox to the engine.
Entry link: Bell Housing


A benign condition is one that is not usually serious or harmful. Zero emissions for example.
Entry link: Benign


Hydrocarbon fuel additive and octane improver.
Entry link: Benzole

Bevel Gears

Gears cut at an angle from the periphery so that they can transmit a drive through an angle. An example is the final drive crown wheel and pinion.
Entry link: Bevel Gears


Brake Horse Power
Entry link: BHP

Bi-Metal Spring

A spring made of two metals that expand differently with temperature change. This changes the tension as temperature changes.
Entry link: Bi-Metal Spring


Towards one side or one polarity.
Entry link: Bias


Favouring one thing over another.
Entry link: Biased

Big End

End of the con rod that fits to the crankshaft.
Entry link: Big End

Big End Bearings

The journals and shell bearings on a crankshaft that carry the big ends of the connecting rods.
Entry link: Big End Bearings

Bimetal Strip

Two metals bonded together so that when heated, the different rates of expansion cause the strip to bend. The amount of bend is proportional to the temperature.
Entry link: Bimetal Strip

Bimetal Thermostatic Spring

A spring that changes tension with temperature.
Entry link: Bimetal Thermostatic Spring

Bimetalic Valve

See Bi-metalic Valve.
Entry link: Bimetalic Valve

Bimetallic Valve

A valve that operates when a temperature change moves a bimetal strip.
Entry link: Bimetallic Valve


A system of numbering using 0 and 1 and used in computer operating systems.
Entry link: Binary

Binary Counter

An electronic device that counts in binary (1s and 0s) by using logic gates and basic memory devices.
Entry link: Binary Counter

Binary digit

A binary digit or bit is the basic unit of information in computing and telecommunications; it is the amount of information that can be stored by a device or other physical system that can normally exist in only two distinct states - 1 or 0, on or off for example.
Entry link: Binary digit


The component in a paint material that forms the film. So-called because it binds the pigment and any additives present into a solid durable film.
Entry link: Binder


Term used to describe one component sticking or rubbing against another.
Entry link: Binding


The capacity of a material to decompose over time as a result of biological activity, especially to be broken down by microorganisms.
Entry link: Biodegradability


A binary digit or bit is the basic unit of information in computing and telecommunications; it is the amount of information that can be stored by a device or other physical system that can normally exist in only two distinct states - 1 or 0, on or off for example.
Entry link: Bit

Black box

Equipment that records information about the performance of an aircraft during flight – or a vehicle during its normal use.
Entry link: Black box

Blade Connector

An electrical cable connector consisting of a blade and spring sided socket.
Entry link: Blade Connector

Blanking Plugs

Screwed plugs used to blank off or block off a test port or adjustment point.
Entry link: Blanking Plugs


The act of removing air from a liquid system.
Entry link: Bleed

Bleed Nipple

A small nipple valve that allows connection of a pipe and is operated by loosening.
Entry link: Bleed Nipple


A defect in which pigment from a lower coat of paint diffuses into an upper coat and discolours the latter. A non-bleeding colour is one that is not soluble in materials used over it and consequently does not work up into succeeding layers. Body filler may also cause bleeding if an excessive amount of hardener is added.
Entry link: Bleeding


Repainting of panels or parts of panels and fading out the new colour onto adjacent prepared panel work to render the repair invisible. Normally only carried out on basecoat-and- clear finishes, as it is very difficult to blend a direct gloss paint finish.
Entry link: Blending

Blending Flaps

Flaps used to mix hot/cold and fresh/recirculated air in a heater system.
Entry link: Blending Flaps

Blipped Throttle

Description of a 'quick press' of the throttle to make the engine rev up.
Entry link: Blipped Throttle


The development of hollow bubbles or water droplets in a paint film. Blistering is usually caused by the expansion of air or moisture trapped beneath the film. It can occur rapidly or any time after application as the paint film ages. Blistering may also occur from the presence of unreacted acid within the paint film.
Entry link: Blistering

Block diagram

A diagram of a system, in which the main parts or functions are represented by blocks connected by lines, which show the relationships between the blocks.
Entry link: Block diagram

Blocker Bar

General term used to describe a bar that prevents an action of some kind.
Entry link: Blocker Bar


A powder-like deposit which sometimes forms on the surface of a paint. It is often the result of a solvent component partly dissolving the pigment(s) and then depositing them on the surface when the temperature is below the 'dew point',( i.e. the temperature at which moisture will condense on the surface)
Entry link: Blooming

Blow Back

Ignition of fuel in the inlet manifold causing a flame to rise out of the air intake through the carburettor.
Entry link: Blow Back

Blower Motor

A motor that uses a fan to assist in moving air.
Entry link: Blower Motor


Wireless Technology. A chip is responsible for the transmission of data between a wide range of devices (mobile phone and hands-free system) through short range digital two-way radio.
Entry link: Bluetooth


Trade name for 'blue' headlight bulbs produced by Philips.
Entry link: BlueVision


The appearance of whitish or "cloudy" areas in a paint finish, caused by absorption and retention of moisture in a drying paint film.
Entry link: Blushing


Barometric/Manifold Absolute Pressure Sensor
Entry link: BMAP

Bodied Vehicles

A bodied vehicle is defined as ‘a vehicle with a structure consisting/comprising of a floor pan and panels which, with a roof fully encloses the vehicle occupants and without a roof encloses them other than where the roof would be’. As a guide, if the driver sits in the vehicle with surrounding structure it would be classed as bodied.

Entry link: Bodied Vehicles


Main portion of motor car.
Entry link: Body

Body Filler

A heavy-bodied 2K plastic filler material which cures very hard and is used to fill small dents in metal and plastic panel work.
Entry link: Body Filler


Thickening of paint in the can, usually due to evaporation of solvents or volatile material because of poor fitting lids or exposure to heat or air.
Entry link: Bodying


Attraction between two things such as to cause them to stick together.
Entry link: Bond

Bonding Cables

Cables or wires used to connect different panels together.
Entry link: Bonding Cables

Bonding Resin

Adhesive often used on friction linings.
Entry link: Bonding Resin


Brake on/off switch
Entry link: BOO

Boost Pressure

The amount of increase above atmospheric pressure provided by a supercharger.
Entry link: Boost Pressure

Booster Fan

See blower motor.
Entry link: Booster Fan


Usually made of rubber, a cover for a moving component such as a track rod end.
Entry link: Boot


A rubber (or similar) boot used to cover working components. It is used to keep dirt out and in some cases lubrication in place. Also slang for alligator...
Entry link: Boots/Gaiters

Bore (cylinder)

The internal part of a hollow cylinder in which a piston is located.
Entry link: Bore (cylinder)

Boring Bar

Used to cut cylinder bores.
Entry link: Boring Bar

Boron steel

Boron steels possess hardenability equivalent to that of much higher carbon steels and more expensive low alloy heat treatable steels. Tempering toughens boron steels. The addition of only 0.001-0.003% soluble boron to a suitably protected base steel can produce an increased hardenability compared other steels.
Entry link: Boron steel


Robert Bosch GmbH is a technology-based corporation which was founded by Robert Bosch in Stuttgart, Germany in 1886.
Entry link: Bosch


A reinforcing section around a cylindrical bore in a component.
Entry link: Boss

Bottom Dead Centre

The position of the crankshaft when the piston is at its lowest position in the cylinder.
Entry link: Bottom Dead Centre


Vehicle body suspension movement when hitting bumps.
Entry link: Bounce

Bounce Test

A manual test of suspension dampers (shock absorbers) by pushing down on the suspension and observing the oscillations when released.
Entry link: Bounce Test


Movement of an electric window as it hits an obstruction - and bounces back (opens again).
Entry link: Bounce-back

Boundary lubrication

This form of lubrication is essentially a breakdown of hydrodynamic action. At high loads or low speeds, the pressure of the oil film cannot prevent metal-to-metal contact. So the opposing surfaces partially ride on an oil film and partially rub together as surface high points come in contact. Lubrication is provided by lubricant decomposition products or surface-active additives which form a thin, soft, solid film on the metal surfaces and prevent metal-junction adhesion.
Entry link: Boundary lubrication

Bourdon Tube

A U shaped tube used to measure vacuum.
Entry link: Bourdon Tube

Box Sections

Parts of the vehicle body - chassis and structural members.
Entry link: Box Sections

Boxer Engine

A horizontally opposed engine.
Entry link: Boxer Engine

BP Sensor

A barometric pressure sensor.
Entry link: BP Sensor


Back pressure Sensor
Entry link: BPS


Back Pressure Transducer
Entry link: BPT


(1) Device to retard the motion of a vehicle or to prevent inadvertent movement when parked. (2) Dynamometer for measuring the power of an engine, originally a friction brake by which torque could be measured. Also brake dynamometer (informal).
Entry link: Brake

Brake Accumulator

A pressure container fitted into pumped hydraulic systems to maintain a reserve of pressure if the pump fails. They also smooth out the pump pulses in the system.
Entry link: Brake Accumulator

Brake Adjuster

A mechanical device for taking up the free play in brake components. Can be either manually or automatically operated.
Entry link: Brake Adjuster

Brake Balance

The splitting of brake effort to each axle in relation to the optimum that the axle can provide.
Entry link: Brake Balance

Brake Band

A friction material lined strap around a epicyclic gear annulus. Operated by hydraulic pressure to hold the annulus for gear ratio selection.
Entry link: Brake Band

Brake Booster

See brake servo.
Entry link: Brake Booster

Brake Caliper

The fixed component of a disc brake holding the pistons that apply an inward force to press the brake pads onto the rotor.
Entry link: Brake Caliper

Brake Cylinder

The wheel cylinders of hydraulic brakes in the brake unit.
Entry link: Brake Cylinder

Brake Drum

Rotating drum inside which brake shoes operate.
Entry link: Brake Drum

Brake Fade

Reduction of braking effort resulting from overheating of friction surfaces, or other transient effect.
Entry link: Brake Fade

Brake Fluid

A special liquid used in hydraulic brake systems. Always check data because some types should not be mixed.
Entry link: Brake Fluid

Brake Horsepower (bhp)

A measure of the power output from an engine when measured with a dynamometer using a brake applied to the engine flywheel. The engine effort to overcome the braking force gives the bhp value.
Entry link: Brake Horsepower (bhp)

Brake Lines

The hydraulic pipes and hoses of the brake system.
Entry link: Brake Lines

Brake Lining

The friction material attached to brake shoes and pads.
Entry link: Brake Lining

Brake Linkage

A general term to describe components that link different parts of the brake system together.
Entry link: Brake Linkage

Brake Pad

A steel plate with a bonded friction lining used on disc brakes. Similar to the brake shoe of a drum brake.
Entry link: Brake Pad

Brake Rollers

Rollers used to drive the wheels of a vehicle for brake testing purposes.
Entry link: Brake Rollers

Brake Servo

A mechanism (vacuum or hydraulic) that increases the braking effort applied by the driver.
Entry link: Brake Servo

Brake Shoes

Part of drum brake carrying linings.
Entry link: Brake Shoes

Braking Effort

The force applied to the brakes.
Entry link: Braking Effort

Braking Thrust

Forces that are caused by braking.
Entry link: Braking Thrust

Breakout Box

A terminal box for carrying out diagnostic tasks on electrical and electronic systems.
Entry link: Breakout Box

Bridge Rectifier

A type of rectifier using four or more diodes to give full wave rectification.
Entry link: Bridge Rectifier


A characteristic of undercoat performance that occurs when a scratch or surface imperfection is not completely filled, leaving a cavity underneath. It i caused by under-reducing the primer or using too fast a solvent and can lead to the appearance of sand scratches in the finished repair.
Entry link: Bridging


The formation of a metallic-appearing haze on a paint film.
Entry link: Bronzing

Brush End Plate

A plate used to hold brushes in contact with a commutator.
Entry link: Brush End Plate


Pieces of carbon or metal ending in wires or strips. Contacts onto rotating slip-rings or generator/motor commutators.
Entry link: Brushes


Before Top Dead Centre
Entry link: BTDC

BTDC - Before Top Dead Center

BTDC - Before Top Dead Centre.
Entry link: BTDC - Before Top Dead Center

BTDC - Before Top Dead centre

The position of the crankshaft before the piston has passed the top of the cylinder and is still on the way up.
Entry link: BTDC - Before Top Dead centre


British Thermal Units
Entry link: Btu


A technique used to polish an area to remove sanding marks or surface imperfections (see Polishing).
Entry link: Buffing

Buffing Compound

Soft paste containing various grades of fine abrasives suspended in a neutral medium, used to eliminate fine scratches and polish the topcoat.
Entry link: Buffing Compound


The amount of paint film deposited on a substrate (the depth or thickness of which is measured in microns).
Entry link: Build


Substantial structural panel of vehicle body in front of passenger compartment. Also known as a firewall.
Entry link: Bulkhead

Bump Cap

A hard hat.
Entry link: Bump Cap

Bump Steering

Steering action that results from hitting a bump.
Entry link: Bump Steering

Bump Stop

A rubber spring that limits and dampens the movement of a spring to prevent excessive deflection and spring damage.
Entry link: Bump Stop


The ability to float in liquid or in air.
Entry link: Buoyancy


Term used to describe rough edges on metal components.
Entry link: Burrs


A motor vehicle which is constructed or adapted to carry more than eight seated passengers (see also Minibus).

Entry link: Bus


Cylindrical sleeve forming a bearing surface for a shaft or pin.
Entry link: Bush

Bushes (rubber)

A metal and rubber composite bearing that provide both a limited range of movement and insulation from road vibration.
Entry link: Bushes (rubber)

Buss Bar

A conductor in a fuse box or other electrical distribution device.
Entry link: Buss Bar


Synthetic rubber impervious to oxygen.
Entry link: Butyl

Butyl Acetate

A medium-evaporating solvent used in paint.
Entry link: Butyl Acetate


A secondary route in a system that allows gas, liquid or electricity to flow outside of the main route.
Entry link: Bypass

Bypass Valve

In a lubrication system a valve that allows oil to bypass a filter.
Entry link: Bypass Valve



Entry link: C

C Classification (SAE)

Engine oil suitable for diesel engines. The second letter in the classification denotes the quality and minimum conditions that the oil must meet.
Entry link: C Classification (SAE)


Cold filter plugging point. Applies to diesel fuel with a cold weather additive."
Entry link: C.F.P.P


Computer Controlled Coil Ignition
Entry link: C3I

Cadence braking

An emergency braking procedure using rhythmic application and release of the brakes to strike a compromise between slowing down with locked wheels, so retaining the ability to steer.
Entry link: Cadence braking


A metal used in the manufacture of durable but expensive red and yellow pigments.
Entry link: Cadmium


A soft grey metallic element used a component in driers and pigments.
Entry link: Calcium

Calcium Carbonate

An extender pigment, also known as "whiting."
Entry link: Calcium Carbonate


The act of making sure a piece of measuring equipment is accurate. Often this is done by checking it against equipment that is known to be good.
Entry link: Calibrate


This means that a piece of measuring equipment is accurate. Often this is done by checking it against equipment that is known to be good.
Entry link: Calibrated

Calibrated Aperture

An accurate size hole to control flow.
Entry link: Calibrated Aperture

Calibrated Float

The float used in a hydrometer. It is designed to work accurately (calibrated) usually at 15 degrees Celsius.
Entry link: Calibrated Float

Calibration Resistor

A variable resistance that is used to set the basic position of a circuit.
Entry link: Calibration Resistor


In a disc brake system, the mechanism that brings brake pads to bear on the disc by a clamping or pinching action, similar to that of the jaws of a Vernier caliper.
Entry link: Caliper

Caliper Piston

A slave cylinder in a brake caliper.
Entry link: Caliper Piston


Calibration Pack
Entry link: CALPAK


(1) A shaped or profiled component that produces linear or angular motion or lift of a follower. Except in the steering box, most automotive cams are in the form of non-circular wheels which impart motion to the follower by their rotation. (2) A camshaft (informal). Misleading usage, as for instance twin cam to describe an engine with two camshafts.
Entry link: Cam

Cam Belt

Belt, usually made of reinforced rubber, which drives the cam from the crank.
Entry link: Cam Belt

Cam Linkage

A cam shaped (egg shaped) part.
Entry link: Cam Linkage

Cam Lobe

High point of a cam which operates components.
Entry link: Cam Lobe

Cam Plate

A plate with one or more raised areas in the shape of a cam. Used in rotary diesel injection pumps to supply high pressure injection.
Entry link: Cam Plate

Cam Ring

A shaped ring with a cam shape.
Entry link: Cam Ring


(1) Convex arched curvature of a (usually horizontal) surface. (2) Average curvature of the chord wise section of an aerofoil. (3) Mildly arched profile of a road or pavement. (4) Inclination of the plane of a wheel to the vertical plane of symmetry of a vehicle. Camber is considered positive if the wheel leans out towards the top, and negative if it slopes inward.
Entry link: Camber


Shaft on which suitably phased cams are mounted, as for example to operate intake and exhaust valves of an engine. In four-stroke engines the camshaft rotates at half crankshaft speed.
Entry link: Camshaft


Controller Area Network. A protocol for a multiplexed system of control and communication on a vehicle.
Entry link: CAN


The actual circuit on which the CAN signal/message is transmitted. It is usually a pair of wires but fibre optics have been used.
Entry link: CAN Bus

CAN message

The information transmitted on a data bus from one node to another.
Entry link: CAN message


Canister Purge Solenoid Valve
Entry link: CANP

Cap (Tire Valve)

Air Valve. Secondary air valve for an inflated tire.
Entry link: Cap (Tire Valve)


An ability to store an electrical charge in two conductors separated by an insulator.
Entry link: Capacitance


Electrical/electronic device consisting of two plates separated by an insulator. It is capable of holding a charge.
Entry link: Capacitor

Capacity (engine)

Applied to the sum total of the swept volumes for all cylinders in an engine. Also known as 'total displacement'.
Entry link: Capacity (engine)

Carbon Black

A black pigment manufactured by collecting the carbon resulting from incomplete combustion of natural gas.
Entry link: Carbon Black

Carbon Monoxide (CO)

Polluting, odourless, toxic (poisonous) gas produced by incomplete combustion of fuel.
Entry link: Carbon Monoxide (CO)


See Carburettor.
Entry link: Carburetor


Device for Vaporizing liquid fuel and mixing it in appropriate proportions with a stream of air, prior to combustion in an engine.
Entry link: Carburettor

Cardan Joint

A drive shaft universal joint consisting of two yokes and a cross bearing. Also Hooke's joint.
Entry link: Cardan Joint


Crank Angle Sensor
Entry link: CAS


A metal forming process where molten metal is poured or injected into a mould.
Entry link: Casting


(1) Originally an undercarriage member with a vertical pivot axis behind which the wheel trailed, so that the wheel aligned itself to its direction of motion. (2) Steering geometry, parallel to the direction of travel, in which the steering pivot is inclined away from the vertical in order to give the effect of castor as described in 1. Also castor offset and castor trail. Small pivoting wheel attached to piece of furniture to facilitate movement.
Entry link: Castor

Castor Angle

Angle in side elevation between the steering and vertical axis.
Entry link: Castor Angle


A substance that causes a chemical reaction when it is mixed with another substance.
Entry link: Catalyst

Catalytic Converter

Uses platinum, palladium and rhodium to change pollutants in exhaust gases to harmless substances.
Entry link: Catalytic Converter

Catch Up

The process by which testing test data recorded while testing under Emergency Testing is subsequently entered via the VTS Device.

Entry link: Catch Up


A negative connection.
Entry link: Cathode

Cationic electrodeposition

One of the electro-coating (E-coat) methods in which the body is charged negatively and the paint positively. The cationic method is superior to the anionic method in terms of corrosion resistance. Frequently used for OEM primer application.
Entry link: Cationic electrodeposition


Sealing used in joints to prevent the passage of fluid (commonly moisture) or gas.
Entry link: Caulking


The formation of cavities in a structure or of gas bubbles in a liquid, or of a vacuum or partial vacuum as between a body moving in a fluid and the fluid.
Entry link: Cavitation


Cubic Centimetres
Entry link: CC


Cold cranking amps (a rating for batteries)
Entry link: CCA


Comite des Constructeurs d'Automobile du Marche Commun. The European organisation that set standards for engine lubricants. This organisation has been replaced by ACEA (Association des Constructeurs Europeens d'Automobiles).
Entry link: CCMC


Compact Disk Read Only Memory. Stores up to 800Mb of data. The data is 'read only' which means that you cannot change or overwrite it.
Entry link: CD ROM


Capacitor Discharge Ignition
Entry link: CDI

CDI (Ignition)

Capacitor discharge ignition system that uses a capacitor to produce the high tension for arcing across the electrodes of the spark plug.
Entry link: CDI (Ignition)


Cold Engine Air Bleed
Entry link: CEAB


Central Electronic Control Unit
Entry link: CECU


That part of a battery made from two dissimilar metals and an acid or alkali solution. A cell stores chemical energy for use later as electrical energy.
Entry link: Cell

Cell Caps

Removable covers for a battery cell.
Entry link: Cell Caps

Center Bearings

See Centre Bearings.
Entry link: Center Bearings

Center of Gravity

See Centre of Gravity.
Entry link: Center of Gravity

Centre Bearings

Bearings usually used to support a rotating shaft - at its centre. Many RWD propshafts have a centre bearing for example.
Entry link: Centre Bearings

Centre Link

The centre track rod of a three-part steering system which connects the steering box drop arm to the idler and the two outer track rods.
Entry link: Centre Link

Centre of Gravity

The point about which an object would balance in all directions. Also the point about which it can be said that gravity is acting on something.
Entry link: Centre of Gravity

Centre Point Steer

Steering geometry, parallel with the vehicle axis, in which wheel camber and steering swivel axes meet at the centre line of a steered wheel at ground level.
Entry link: Centre Point Steer

Centrifugal Force

The outward movement felt as a car turns a sharp corner.
Entry link: Centrifugal Force

Centrifugal Unit

Mechanical system using weights attached to a shaft. These move out against spring force as the shaft speed increases. Senses shaft speed for ignition advance and diesel pump speed.
Entry link: Centrifugal Unit


Cold Enrichment Rod
Entry link: CER


Cold Engine Sensor Switch
Entry link: CESS

Cetane Number

Applies to diesel fuels as a measure of the delay in ignition after injection. A higher number indicates a shorter delay.
Entry link: Cetane Number

Cetane Rating

See cetane number.
Entry link: Cetane Rating


Central Fuel Injection
Entry link: CFI

CFI (Fuel Injection)

Usually centre point fuel injection system but sometimes used for continuous fuel injection.
Entry link: CFI (Fuel Injection)


Cubic Feet Per Minute
Entry link: cfm


Used to describe the unintentional action of one component rubbing against another.
Entry link: Chaffing


The degradation of a paint film by gradual erosion of the binder, typically due to weathering. It is common in ageing red finishes and is characterized by a pinkish haze and loose pigment particles on the surface of the paint
Entry link: Chalking


A soft suede leather formerly from the skin of the chamois antelope but now more often made from sheepskin.
Entry link: Chamois

Charcoal Canister

A part of a fuel evaporative (EVAP) system. The charcoal absorbs petrol vapour during fuel tank venting and returns the fuel to a reverse air flow and into the engine under specific conditions.
Entry link: Charcoal Canister

Charge Current

See charge rate.
Entry link: Charge Current


Process of building up the level of charge in a battery or capacitor.
Entry link: Charging

Charging Rate

The recommended rate of charge for a battery. Usually one tenth of the amps in the Amp hour rate for one and a half times the hours for a fully discharged battery.
Entry link: Charging Rate


Structural lower part of a vehicle to which the running gear and body are attached. The true chassis is now evident only in larger vehicles.
Entry link: Chassis

Check Valve

A one way valve, using a plate or ball and spring, that permits fluid flow in one direction only. Used in hydraulic systems to retain a residual pressure.
Entry link: Check Valve


A type of paint film defect in which cracks in the film begin at the surface and progress downward. The result is usually a straight v-shaped crack which is narrower at the bottom than the top.
Entry link: Checking


A checksum is a count of the number of bits in a transmission unit that is included with the unit so that the receiver can check to see whether the same number of bits arrived. If the counts match, then one can assume that the complete transmission was received.
Entry link: Checksum

Chemical Bond

A reaction between atoms that causes a force such as to create a bond.
Entry link: Chemical Bond

Chemical Cartridge Respirator

A respirator which uses a cartridge containing various chemical substances to purify inhaled air of certain gases and vapours.
Entry link: Chemical Cartridge Respirator

Chemical Staining

Spotty discolouration of the topcoat sometimes caused by environmental conditions (acid rain, tree sap, etc.) It can also be caused by improper activation of body filler which leads to staining in the subsequent layers of topcoat.
Entry link: Chemical Staining

Chemical Treatment

A process that uses chemical to bring about a change in something.
Entry link: Chemical Treatment


Description of an integrated circuit where the circuit is built on a silicon chip.
Entry link: Chip


Small flakes of a finish losing adhesion from the substrate. Usually caused by the impact of stones or hard objects.
Entry link: Chipping


A restriction in a carburettor. The term is used to describe either the venturi as in single or twin choke carburettor, or for the cold start device.
Entry link: Choke

Choke Flap

The butterfly type valve that restricts the flow of air.
Entry link: Choke Flap

Chopper Module

An electronic circuit or unit that switches a supply on and off rapidly.
Entry link: Chopper Module


The level of saturation or intensity and richness of a colour. De-saturated or "dirty" colours have less chroma; saturated or "clean" colours have more chroma.
Entry link: Chroma


A chemical compound used as a component in primers to provide corrosion protection to metal.
Entry link: Chromate

Chromate Rinse

Newly manufactured vehicle bodies are completely immersed in a chromic acid solution after zinc or iron phosphating to passivate the metal at the base of cracks and pinholes in the phosphate. Chromate rinsing, as used in modern mass-production paint preparation, will greatly increase corrosion resistance.
Entry link: Chromate Rinse


cylinder identification sensor
Entry link: CID


A complete conducting path.
Entry link: Circuit

Circuit Board

A board used to construct an electronic circuit.
Entry link: Circuit Board

Circuit Breaker

A switch to turn off the current flow in a circuit. Can be manually or automatically operated.
Entry link: Circuit Breaker

Circuit diagram

A diagram using symbols for electrical and electronic components that represents a real circuit.
Entry link: Circuit diagram


The boundary line of a circle.
Entry link: Circumference


Continuous Injection System
Entry link: CIS


Crankshaft Position Sensor
Entry link: CKP

CKP Sensor

Abbreviation for the crankshaft position sensor.
Entry link: CKP Sensor

Clamp Plate

A simple plate to hold another item securely.
Entry link: Clamp Plate


To make clear.
Entry link: Clarify


Clay is a naturally occurring material composed primarily of fine-grained minerals. It is used in some cases to act as a very fine abrasive for improving paintwork.
Entry link: Clays


Material used to remove dirt and other impurities from a substrate prior to painting.
Entry link: Cleaner

Clear Coat

The transparent, non-pigmented top coat that is applied over a coloured base coat paint. Most modern cars have factory-applied clear coat paints. Clear coat paint increases paint durability, gloss, and resistance to harmful environmental effects such as ultra-violet radiation.
Entry link: Clear Coat


A gap between two components.
Entry link: Clearance

Clearance Fit

The relationship between the dimensions of two components where one fits inside the other. In this instance the fit is one where the inner dimension of the outer component is greater than the outer dimension of the inner component.
Entry link: Clearance Fit

Clearance Size

A drilling size slightly larger than the nominal size of a thread.
Entry link: Clearance Size

Clearance Volume

The space above a piston at top dead centre in a cylinder. Includes the combustion chamber and any other volume formed by the thickness of gaskets, etc.
Entry link: Clearance Volume


A temporary area used to store copied information.
Entry link: Clipboard

Clock spring

These are generally made of rectangular section material, flat strip, with round edges. They are general used as brush springs in D.C. motors. Also known as spiral springs
Entry link: Clock spring


Condition where abrasive paper becomes clogged by the abraded surface coating.
Entry link: Clogging

Closed Circuit

Applied to an electrical circuit when the switch is 'on' or the circuit is continuous.
Entry link: Closed Circuit

Closed Loop

A system where a change in the output causes a changed input which in turn changes the output and so on...
Entry link: Closed Loop

Closed Loop System

Electronically controlled system, which adjusts settings by feedback from sensor signals that are monitoring the performance of actuators in the system and comparison with the pre-programmed map.
Entry link: Closed Loop System


The formation or presence of a haze in a liquid such as a paint film.
Entry link: Clouding


A device to allow drive to be connected and disconnected. In a starter motor a clutch is used to only allow drive to pass one way - starter to engine, NOT engine to starter.
Entry link: Clutch

Clutch (Transmission)

Disengages / Engages drive from the engine.
Entry link: Clutch (Transmission)

Clutch Fork

See Release Fork.
Entry link: Clutch Fork

Clutch Linkage

Mechanism to connect the pedal to the clutch release bearing. May be cable, electrically or hydraulically operated.
Entry link: Clutch Linkage

Clutch Pack

A set of friction plates and pressure plates in a multi-plate clutch.
Entry link: Clutch Pack

Clutch Plate

The friction plate used as part of a clutch.
Entry link: Clutch Plate


Camshaft Position Sensor
Entry link: CMP

CMP Sensor

Abbreviation for the camshaft position sensor.
Entry link: CMP Sensor


Carbon Monoxide
Entry link: CO


Carbon Dioxide
Entry link: CO2


A motor vehicle which is constructed or adapted t carry more than 16 seated passengers, with a DGW of more than 7,500kg and a maximum speed in excess of 60mph.

Entry link: Coach


Coaching is a method of directing, instructing and training a person or group of people, with the aim to achieve some goal or develop specific skills.
Entry link: Coaching


The fusing or flowing together of liquid particles. The term is frequently applied to waterborne coatings, which require coalescence to form a continuous film.
Entry link: Coalescence


Driving on very light throttle at a constant speed.
Entry link: Coasting


The act of applying paint or the actual film left on the substrate by an applied paint. A single coat may be produced by two passes of a spray gun, one overlapping the other in half steps. A double coat is two single coats with little or no flash-off time between them.
Entry link: Coating


The tendency of sprayed paint to form strings or strands rather than droplets as it leaves the gun. May be caused by too fast or improper solvent, paint too thick or air pressure too low.
Entry link: Cobwebbing

Coefficient of Friction

A value between 0 and 1 that indicates the ability of two materials to grip each other when sliding or rolling in contact with other.
Entry link: Coefficient of Friction

Coil (Ignition)

An electrical transformer that increases the battery voltage to a high tension capable of arcing across the gap of spark plug electrodes.
Entry link: Coil (Ignition)

Coil Spring

A spring that consists of a single length of bar wound into a helix (coil).
Entry link: Coil Spring

Cold Cranking Rating

Applies to a battery's ability to provide a minimum current for a minimum time for starting a cold engine.
Entry link: Cold Cranking Rating

Cold Start Enrichment

An increase in the amount of petrol mixed with the air under cold starting conditions.
Entry link: Cold Start Enrichment

Cold Start Valve

An extra valve used only when starting from cold.
Entry link: Cold Start Valve

Cold Starting

Cranking the engine so that it will start and run under cold conditions.
Entry link: Cold Starting


Cracking of a paint film resulting from a sudden drop in temperature, or repeated cycling from high to low to high temperatures.
Entry link: Cold-Cracking

Cold-start Valve

An extra valve used only when starting from cold.
Entry link: Cold-start Valve


Terminal of a transistor that becomes conductive to the emitter when the base is energised.
Entry link: Collector


Small half-round and tapered components used to fix a valve stem to its cap.
Entry link: Collet


The visual appearance of an object that can be described in terms of hue, value, and chroma. Colours are seen differently by different people and under different lighting conditions.
Entry link: Colour

Colour Coat

The single-stage or basecoat that provides the visible colour of a coating system.
Entry link: Colour Coat

Colour Match

Achieved when the applied colour duplicates all aspects of the original colour's appearance in terms of hue, value, and chroma.
Entry link: Colour Match

Colour Retention

The ability of a paint to maintain colour under exposure to light, heat, moisture or other conditions of use.
Entry link: Colour Retention

Colour Sanding

The sanding of a cured or dried paint film to prepare it for polishing or recoating.
Entry link: Colour Sanding


The burning of fuel in air.
Entry link: Combustion

Combustion Chamber

Area above the piston when it is at TDC where the combustion takes place.
Entry link: Combustion Chamber

Combustion Knock

Advanced or quick detonation of fuel in a cylinder where the resultant pressure rise causes a shock wave through the piston, crankshaft and engine block.
Entry link: Combustion Knock

Combustion Stroke

The third stroke of the four stroke cycle when the fuel is burnt to produce heat energy, expansion of the air/fuel charge and power on top of the piston. Also known as the power stroke.
Entry link: Combustion Stroke


This is a process of transferring information from one entity to another. An exchange of thoughts and information if human.
Entry link: Communication


Rotating contacts for electrical windings on a generator or motor armature.
Entry link: Commutator


A strategy that involves adjusting something up or down to more closely approximate the required or ideal value.
Entry link: Compensating


Provides equal force to mechanically braked wheels.
Entry link: Compensator

Compliance Coating

A coating whose volatile organic compound (VOC) content does not exceed that allowed by regulations. Compliance coatings may be waterborne, low solvent, or powder.
Entry link: Compliance Coating

Composite Materials

Material made up of constituents that remain recognisable.
Entry link: Composite Materials


Place where cars are taken when they die, or dogs when they get lost...A chemical where the two or more elements they contain combine at the molecular level - salt for example is a compound of sodium and chlorine (sodium chloride).
Entry link: Compound

Compound Gear Train

Two or more pairs of gears.
Entry link: Compound Gear Train


The use of an abrasive material, either by hand or machine, to smooth and enhance the gloss of the applied topcoat.
Entry link: Compounding


The reduction in volume of a gas when it is squashed. The gas pressure increases and the temperature rises.
Entry link: Compression

Compression Ignition (CI)

Fuel ignited by heated air (diesel).
Entry link: Compression Ignition (CI)

Compression Ratio

The ratio between the TOTAL volume of a cylinder (swept volume plus clearance volume) and the CLEARANCE volume (volume above the piston at TDC - the combustion chamber).
Entry link: Compression Ratio

Compression Ring

A piston ring that helps to contain combustion pressure.
Entry link: Compression Ring

Compression Spring

A spring that is designed to provide force when compressed.
Entry link: Compression Spring

Compression Stroke

The second stroke of the four stroke cycle when air or the fuel/air mixture is compressed. Compression is necessary for clean and efficient combustion of the fuel.
Entry link: Compression Stroke


Electrically or mechanically driven pump used to increase pressure of a gas or liquid.
Entry link: Compressor

Compressor Wheel

Part of a turbocharger that pumps extra air into the intake and therefore the engine.
Entry link: Compressor Wheel


Must be completed.
Entry link: Compulsory

Computer Application

Programs such as Word, Excel and PowerPoint.
Entry link: Computer Application

Computer Crash

An event that causes the computer to become inactive. This can often result in the loss of unsaved work.
Entry link: Computer Crash

Con Rod

Short for connecting rod, this joins the pistons to the crankshaft.
Entry link: Con Rod


A term that describes objects that revolve or are fitted around a common centre.
Entry link: Concentric


Expressing a lot but in few words.
Entry link: Concise


1. Part of an air conditioning system positioning in the outside air stream. It gives off heat to atmosphere as a refrigerant condenses. 2. Alternative name for a capacitor in an ignition system.
Entry link: Condenser

Condenser (A/C)

A heat exchanger in an air conditioning system that is similar to, and fitted in front of, the coolant radiator where it passes heat energy to the air stream passing through it. Operates by condensation of the refrigerant from gas to liquid by pressure and heat loss.
Entry link: Condenser (A/C)

Condenser (Ignition)

An electrical capacitor that is used in a contact breaker ignition system.
Entry link: Condenser (Ignition)


Transfer of electrical or heat energy along material.
Entry link: Conduction


A material that allows free movement of electricity or heat through it.
Entry link: Conductor

Conductor Foil

General term to describe a type of 'flat' wiring harness.
Entry link: Conductor Foil

Cone Clutch

A simple clutch shaped like a cone. Used as part of a synchromesh mechanism.
Entry link: Cone Clutch

Cone Pulley

A pulley shaped like a cone such as to allow different ratios to be set by the position of a drive belt.
Entry link: Cone Pulley

Confidential Information

Information that is private and should be protected.
Entry link: Confidential Information

Connecting Rod

The engine component that joins the piston to the crankshaft.
Entry link: Connecting Rod

Constant Velocity Joint

A drive shaft joint that transmits drive through an angle without changes in speed.
Entry link: Constant Velocity Joint

Construction and Use

The UK Construction and Use Regulations that cover the legal requirements on manufacturers and users of road vehicles.
Entry link: Construction and Use

Constructive feedback

A way of giving feedback to somebody so that they feel valued and that they can improve what they did based on your comments.
Entry link: Constructive feedback


The rate at which a vehicle uses fuel.
Entry link: Consumption

Contact Breakers

Mechanical spring-loaded switch located in the distributor of an ignition system and actuated by a rotating cam. It makes or breaks the ignition circuit to control the coil output and delivery of a spark to the spark plug.
Entry link: Contact Breakers


Something which contaminates; an impurity; foreign matter
Entry link: Contaminant


Any polish, wax, tree sap, tar, oil, etc., that would damage the paint film or spoil the adhesion of a new paint film.
Entry link: Contaminants


The condition of an electrical circuit when a current will flow.
Entry link: Continuity

Continuous Injection

Injectors that inject or 'squirt' all the time.
Entry link: Continuous Injection

Continuous Injection Systems

Injection systems where the supply to the inlets is active all the time but may only 'spray' on the intake stroke due to the lower pressure.
Entry link: Continuous Injection Systems


(see Mapping)
Entry link: Contouring


Agreement between parties enforceable in law.
Entry link: Contract


A decrease in size. For example, when a metal rod is cooled it decreases in length and diameter. Opposite of expansion.
Entry link: Contraction

Control Flap

A flap that is used to control something! Air temperature for example.
Entry link: Control Flap

Control Plunger

Part of fuel injection system. Regulates fuel delivery against air flow.
Entry link: Control Plunger

Control Pump

A pump that provides a set pressure.
Entry link: Control Pump


Travel of heat by movement in heated fluids due to a reduction in density and consequent rise of the hotter material.
Entry link: Convection

Conversion Coating

Conversion coatings are used on metal parts (such as vehicle bodies) to be painted. They are acidic chemical products used before paint to convert the metal substrate to an iron or zinc phosphate surface. The chemical reaction modifies the metal surface to enhance paint adhesion and corrosion protection
Entry link: Conversion Coating

Conversion Factor

Used to make it easier when converting from one form of ‘measurement' to another.
Entry link: Conversion Factor


To change one expression to another. For example, expressing miles in kilometres.
Entry link: Conversions


An additive used to provide a chemical reaction to cure paint. Also used with some primers to convert them to 'non-sanding' versions, by changing their properties and making them suitable for wet-on-wet procedures.
Entry link: Converter


Liquid made up of water, anti-freeze and inhibitors used to cool an engine in a sealed but circulated liquid system.
Entry link: Coolant


Coil on plug, where a different ignition coil is used for each spark plug on an engine. Also known as direct ignition.
Entry link: COP


A difficult metal substrate to paint. Also used in the manufacture of special decorative pigments and synthetic driers.
Entry link: Copper

Core Plug

A steel plate fitted into a cylinder block or cylinder head casting after the casting sand has been removed in order to produce a fully sealed component.
Entry link: Core Plug


The decomposition of a metal in contact with its environment - a chemical reaction of oxygen and moisture or corrosive materials on a metal surface. Also called oxidation or rusting (on ferrous metals).
Entry link: Corrosion


An acid or other chemical that will chemically react or attack another material.
Entry link: Corrosive


The Control of Substances Hazardous to Health Regulations 2002 is a United Kingdom Statutory Instrument that stipulates general requirements on employers to protect employees and other persons from the hazards of substances used at work by risk assessment, control of exposure
Entry link: COSHH

Cost of production

The actual cost to the manufacturer of producing a vehicle (it does not include mark-up).
Entry link: Cost of production

Cotter Pin

Tapered pin used to hold shafts into housings. May also be used to describe a split pin.
Entry link: Cotter Pin

Counter Gear

See countershaft assembly.
Entry link: Counter Gear

Counter Shaft

An alternative term used to describe the layshaft in a manual gearbox. The shaft in a manual gearbox carrying the gear cluster and meshing with the constant mesh gears.
Entry link: Counter Shaft


An alternative term used to describe the layshaft in a manual gearbox. The shaft in a manual gearbox carrying the gear cluster and meshing with the constant mesh gears.
Entry link: Countershaft


Steering force that acts such as to prevent the wheels moving off their intended line.
Entry link: Countersteer


A pair of equal parallel forces that are opposite in direction. The effect of a couple is to produce or prevent the turning of a body.
Entry link: Couple

Coupling Point

The point or speed at which a torque converter takes up drive.
Entry link: Coupling Point

Courtesy Lights

Lights for the vehicle occupants to use.
Entry link: Courtesy Lights


The amount of area a volume of paint will cover at a certain thickness. Theoretical coverage is described as the number of square metres a coating will cover at 1 mm film thickness.
Entry link: Coverage


General term used to describe a cover.
Entry link: Cowling


See single point injection.
Entry link: CPI


Crankshaft position and speed sensor.
Entry link: CPS


Central processing unit. This relates to the main component in an ECU or computer.
Entry link: CPU


Splitting of a paint film. Cracking usually appears as straight lines which penetrate the entire film thickness and can be caused by over-baking or by application of excessive film builds.
Entry link: Cracking


A term used to describe turning the engine by the starter motor.
Entry link: Crank


The part of the engine that houses the crankshaft and the bearings in which it runs. It can be either a separate part or be integral with the engine block.
Entry link: Crankcase

Crankcase Ventilation

Usually a positive crankcase ventilation (PCV) system that allows any crankcase pressure and oil vapour to be passed into the combustion chamber so that it does not escape into the atmosphere as a pollutant. Early crankcase ventilation consisted of an open vent or breather tube that allowed crankcase gases to be passed out below the vehicle.
Entry link: Crankcase Ventilation


Description of making the engine rotate on the starter motor.
Entry link: Cranked


The process of turning over an engine using a starter motor (or a handle on earlier models!).
Entry link: Cranking


Major rotary component of engine that converts piston movement into rotary movement.
Entry link: Crankshaft

Crankshaft Damper

Usually part of the front pulley. A rubber mounted mass reduced torsional vibration.
Entry link: Crankshaft Damper

Crankshaft Oil Seal

Usually radial lip type seals at the front and rear of the crankshaft.
Entry link: Crankshaft Oil Seal

Crankshaft Pulley

Main drive pulley on the end of the crankshaft.
Entry link: Crankshaft Pulley

Crankshaft Shell

See Shell Bearings.
Entry link: Crankshaft Shell

Crankshaft Web

Counterbalance weights that are opposite the big end bearing journals.
Entry link: Crankshaft Web

Cratering (silicone cratering, see

'Fish Eyes')">Small round depressions in a paint film which may or may not expose the underlying surface. Frequently caused by contamination of the substrate by wax, oils, etc.
Entry link: Cratering (silicone cratering, see


The tendency of a wet paint film to recede from certain areas of a painted surface. Often caused by the presence of contaminants on the surface.
Entry link: Crawling


The formation of surface cracks, often as a fine network, which do not penetrate to the underlying surface of a paint film. Crazing is sometimes caused by the softening effect of solvents from excessive paint coats as in cellulose or acrylic lacquer repair operations.
Entry link: Crazing


A cyclic redundancy check is a method of checking for errors in data that has been transmitted on a communications link.
Entry link: CRC

Crescent Pump

A positive displacement pump made from one externally and one internally toothed gear rotating eccentrically in a housing. Inside the housing, and in the space formed where the teeth are out of mesh, is a crescent shaped block. This divides the gear teeth to create the pumping and carrying chambers of the pump.
Entry link: Crescent Pump


Act of squeezing a connection such as a terminal onto a wire.
Entry link: Crimp

Crimped Joint

Termination of cables by squashing tabs on the terminal around the cable.
Entry link: Crimped Joint


The process of compressing materials to make a join. Usually refers to squeezing a terminal to secure it to a wire.
Entry link: Crimping

Crocodile Clip

Hand operated clip that, like a crocodile, bites under spring pressure to make a contact. Also alligator clip.
Entry link: Crocodile Clip

Cross Member

A chassis or support member that runs across a vehicle frame or chassis.
Entry link: Cross Member

Cross-Coat (double-header)

A method of paint application often used with high solids paint. The technique involves a side-to-side application followed by a top-to-bottom application with very little flash-off time. Also used by some refinishers when they apply 'drop coats' in more than one direction to eliminate striping in metallic and pearlescent finishes.
Entry link: Cross-Coat (double-header)

Cross-draft Booth

A spray booth in which air movement is horizontal from end to end, i.e. fresh (may be heated) air enters at the front of the booth and is extracted at the rear Not considered to be as efficient as downdraught extraction
Entry link: Cross-draft Booth

Cross-pin (Hooke's) Joint

Type of universal joint with a cross pin and two yokes.
Entry link: Cross-pin (Hooke's) Joint


Form of tyre construction in which the casing plies are laid diagonally so that each ply lies at an included angle, usually of more than 40 degrees, to the adjacent ply.
Entry link: Cross-ply


The area exposed if a cut were to be made through the centre of an object.
Entry link: Cross-section


General term used to describe shafts which are fitted across units rather than along or axially.
Entry link: Cross-shafts

Crown Wheel

Bevel gear wheel in which the teeth are set around the periphery, giving the wheel the appearance of a crown. The larger wheel of the crown wheel and pinion bevel pair.
Entry link: Crown Wheel

Cruise Control

A system that keeps the vehicle at a set speed.
Entry link: Cruise Control


Driving at a constant speed under light throttle conditions.
Entry link: Cruising

Crumple Zone

Safety feature of vehicle body, absorbs impacts.
Entry link: Crumple Zone


The arrangement or bonding of atoms in solid materials which form during cooling to give regular structural patterns.
Entry link: Crystalline

Crystalline Structure

The arrangement or bonding of atoms in solid materials which form during cooling to give regular structural patterns.
Entry link: Crystalline Structure


Cold Start Spark Advance
Entry link: CSSA


Cold Start Spark Hold
Entry link: CSSH


Closed throttle.
Entry link: CT


Coolant Temperature Sensor
Entry link: CTS

CTS Sensor

Abbreviation for the engine coolant temperature sensor or switch.
Entry link: CTS Sensor


Choke Thermal Vacuum Switch
Entry link: CTVS

CTX Transmission

Constantly Variable TransaXle.
Entry link: CTX Transmission

Cup Seal

A hydraulic seal with a lip that contains pressure against the lip but will allow a flow in the opposite direction. Used in the cylinders of brake systems.
Entry link: Cup Seal

Curb Idle

Rotational speed of an engine on no-load and minimum throttle setting. Also tick over and idle.
Entry link: Curb Idle


The process, usually a chemical change, by which paint is converted from the liquid to the solid state.
Entry link: Cure

Cured Paint

Paints that have completed the curing process. Cured paints include all factory-applied paints and refinish paints that have air-dried for more than 30 days. Wax application is recommended only for fully cured paints.
Entry link: Cured Paint


Movement of electrically charged particles. Current flow is measured in Amperes.
Entry link: Current

Current Regulator

An electrical or electronic device used in generator circuits to control the output current.
Entry link: Current Regulator

Current Relay

A device that usually incorporates a reed switch. It is activated by current flow through a series winding.
Entry link: Current Relay

Custom Painting

Unique painting, frequently with special effects or designs, normally designed by owner of vehicle and/or the specialist who will be painting the vehicle.
Entry link: Custom Painting


Refers to both the dissolving of solid material in a solvent and the reducing of the viscosity of a liquid by the addition of a thinner.
Entry link: Cut


Process where fuel supply can be stopped, for example when a vehicle is coasting down.
Entry link: Cut-off


See Cut-off.
Entry link: Cutoff

CV (Constant Velocity) Joint

A drive shaft joint that transmits drive through an angle without changes in speed.
Entry link: CV (Constant Velocity) Joint

CV Joint

A drive shaft joint that transmits drive through an angle without changes in speed.
Entry link: CV Joint


Control Vacuum Regulator
Entry link: CVR

CVT (Transmission)

Constantly variable transmission that uses two conical drums and a drive belt between them. The effective diameter of each drum is varied hydraulically in order to change the drive ratio.
Entry link: CVT (Transmission)

Cylinder (Master)

(1) Primary source of pressure in a hydraulic system such as brake or clutch system, containing the piston by which pressure is applied and connected to a source of hydraulic fluid. (2) Primary unit for dispensing hydraulic fluid under pressure in a hydraulic system.
Entry link: Cylinder (Master)

Cylinder (Slave)

Cylinder and piston that, under hydraulic or pneumatic pressure from a master cylinder, actuates mechanical components. For example, the brakes or a clutch.
Entry link: Cylinder (Slave)

Cylinder Balance

A test carried out with diagnostic equipment to make sure each cylinder of the engine is working to its full potential.
Entry link: Cylinder Balance

Cylinder Block

The part of an engine containing the cylinders. The cylinder block may also incorporate the water cooling jackets and provisions for the valve gear.
Entry link: Cylinder Block

Cylinder Bore

The diameter of the cylinder.
Entry link: Cylinder Bore

Cylinder Charging

Process of filling a cylinder during the induction stroke.
Entry link: Cylinder Charging

Cylinder Head

Encloses the top of the cylinder block.
Entry link: Cylinder Head


Cylindrical or tubular chambers in which the pistons of a reciprocating engine or pump are fitted. They are contained in the cylinder block.
Entry link: Cylinders


DA (Dual Action)

Refers to a power sander used for flatting substrates.
Entry link: DA (Dual Action)

DA (Dual Action) Sander

A machine used for random orbital sanding and buffing. The pad of a DA sander travels in a randomized orbital pattern, rather than taking a simple circular path. DA sanders minimize the swirl marks that commonly result from rotary sanding and greatly reduce the time necessary to produce feather-edges.
Entry link: DA (Dual Action) Sander


A device to reduce oscillations or vibrations. A kind of damper.
Entry link: Dampener


Component that reduces the oscillations of a spring in a suspension system. A device that smoothes out fluctuations.
Entry link: Damper


The reduction of oscillations or smoothing out of fluctuations.
Entry link: Damping

Damping Chamber

An air space in which a damper flap moves that acts to reduce oscillations.
Entry link: Damping Chamber

Darlington Circuit

Two transistors connected so that the first switches the second. Used to switch high currents.
Entry link: Darlington Circuit


A damper used on some variable venturi carburettors.
Entry link: Dashpot


In computer science, data is anything in a form suitable for use with a computer. Data is often distinguished from programs. A program is a set of instructions that detail a task for the computer to perform. In this sense, data is thus everything that is not program code.
Entry link: Data

Data Link

General term for a connection to a scanner or similar diagnostic tool.
Entry link: Data Link

Data rate

The actual speed at which data is transmitted.
Entry link: Data rate

Databank link

A connection to an electronic source of data.
Entry link: Databank link


Entry link: dB


Direct Current
Entry link: DC

DC Brushless Motor

A DC Brushless Motor uses a permanent magnet external rotor, three phases of driving coils, one or more Hall effect devices to sense the position of the rotor, and the associated drive electronics.
Entry link: DC Brushless Motor

DC Direct Current

An electrical current that flows in one direction only. Conventionally from the positive pole to the negative pole.
Entry link: DC Direct Current

DC-DC converter

This is an electronic circuit which converts a source of direct current (DC) from one voltage level to another. It actually converts DC to AC to a different voltage AC and then back to DC!
Entry link: DC-DC converter

de Dion suspension

A de Dion suspension uses universal joints at both the wheel hubs and differential, and uses a solid tubular beam to hold the opposite wheels in parallel. Unlike an anti-roll bar, a de Dion tube is not directly connected to the chassis nor is it intended to flex.
Entry link: de Dion suspension


Switched off - usually refers to a coil or relay.
Entry link: De-energised


Used to describe pure, neutral water used for topping up batteries.
Entry link: De-ionised

Dead Axle

A non-driving axle. Supports the vehicle and carries freely rotating wheels.
Entry link: Dead Axle

Dead centre

Top or bottom piston positions in the cylinder when the crankshaft is at 0° or 180° of rotation.
Entry link: Dead centre


Opposite of acceleration. Reducing velocity or speed. Slowing down.
Entry link: Deceleration


Brake Meter for recording rate of deceleration during braking for test purposes.
Entry link: Decelerometer


A number system that uses a base of 10.
Entry link: Decimal

Decimal Place

The position of numbers after (to the right of) the decimal point.
Entry link: Decimal Place

Deck (Block)

The top of the engine block forming the mating face for the cylinder head.
Entry link: Deck (Block)

Dedicated Test Equipment

Equipment made to work specifically with one system or one manufacturer's vehicle range.
Entry link: Dedicated Test Equipment

Deep Socket

Same as a normal socket but longer to allow it to be used on a component such as a spark plug.
Entry link: Deep Socket


Untrue and harmful information.
Entry link: Defamatory


Digital Electronic Fuel Injection
Entry link: DEFI


Applied to springs to indicate the amount of movement away from the original position.
Entry link: Deflection


The gradual or rapid disintegration of a paint film, normally due to weathering. May be simply fading/loss of gloss or can lead to total paint film breakdown
Entry link: Degradation


Cleaning a bare or previously painted substrate by removing greases, oils, and other surface contaminants.
Entry link: Degreasing

Degrees of Advance

Refers to crankshaft rotation degrees as linked to ignition timing.
Entry link: Degrees of Advance


The loss of adhesion between two or more layers of paint, causing material to separate from the painted surface or substrate.
Entry link: Delamination

Delta Wound Stator

An alternator stator winding with the three-phase coils connected at the ends in order to give a large current output.
Entry link: Delta Wound Stator


An expression of the mass of a substance for a given volume, e.g. water has a density of 1kg per litre
Entry link: Density

Desiccant Bag

Chemical used to absorb moisture. Often used in AC systems to remove moisture from the refrigerant.
Entry link: Desiccant Bag


Careful, in-depth cleaning and polishing of a vehicle's surface finish and/or interior surfaces.
Entry link: Detailing


A position holding device consisting of a spring and locking piece that locates in a groove. A locating device for holding sliding gears in mesh in a manual gearbox.
Entry link: Detent


A material intended to assist cleaning. The term is sometimes used to differentiate between soap and other surfactants used for cleaning.
Entry link: Detergent


Ignition of fuel in an engine that is too early or too rapid. Produces a knocking or pinking sound.
Entry link: Detonation


Deceleration Fuel Shutoff
Entry link: DFS


Design Gross Weight – i.e. the maximum gross weight that the vehicle was designed to operate at by the manufacturer. This is normally found on the manufacturer’s plate fixed to the vehicle, or in the case of older or heavier vehicles by a ‘Ministry Plate’. Such plates are not required on all vehicles.

Entry link: DGW


Direct injection of fuel, usually diesel, into the combustion chamber.
Entry link: DI

Diacetone Alcohol

A slow-evaporating solvent for paints.
Entry link: Diacetone Alcohol


The process of determining the fault in a system based on observed or measures symptoms.
Entry link: Diagnostics

Dial Gauge

A gauge used to indicate lateral movement of a component, on a clock (dial) type display.
Entry link: Dial Gauge

Dial Test Indicator

A gauge used to indicate lateral movement of a component, on a clock (dial) type display.
Entry link: Dial Test Indicator


The line that goes through the centre of the circle.
Entry link: Diameter


Flexible disc or membrane which deflects under pneumatic or hydraulic pressure and, in so doing, imparts linear motion to a centrally-located rod or other form of mechanical actuator, as in an air brake or carburettor.
Entry link: Diaphragm

Diaphragm Spring

Dished clutch spring applying clamping force and disengagement linkage.
Entry link: Diaphragm Spring


A book containing a list of words in alphabetical order. Each word has information given about it (i.e., the definition).
Entry link: Dictionary


Tool used to cut an external thread.
Entry link: Die


Used in a capacitor as an insulator between the two conductive plates.
Entry link: Dielectric


Heavy fuel oil for diesel engines. Compression ignition engine.
Entry link: Diesel

Diesel 'Knock'

Engine noise produced by very rapid rise in cylinder pressure following injection and ignition of the fuel in a diesel engine.
Entry link: Diesel 'Knock'


A condition in a petrol engine when it continues to run after the ignition has been turned off. Also known as running on or run on and usually occurs in a very hot carburettor engine where the fuel cannot be fully shut off.
Entry link: Dieseling


Relating to or using a difference. Operating on differences in pressure. Bevel gear set that allows two wheels to rotate at different speeds.
Entry link: Differential

Differential Pressure Valve

A valve that sets its position depending on the difference between two pressures, for example, two fuel pressures or fuel pressure and manifold pressure.
Entry link: Differential Pressure Valve

Differential Pressure Valves

Valves that operate under the control of TWO external pressures or the difference (differential) between them.
Entry link: Differential Pressure Valves

Digilal Converters

See Digital Converter.
Entry link: Digilal Converters


A number.
Entry link: Digit


A signal current with either an 'on' or 'off' voltage. Digital instruments which show a numerical value.
Entry link: Digital

Digital Converters

Electronic devices that convert analogue signals to digital or digital signals to analogue.
Entry link: Digital Converters


A liquid which increases the capacity of a solvent for the binder. Diluents cannot dissolve the binder themselves. They are usually used to control viscosity or flash-off times.
Entry link: Diluent

Dim-dip relay

A switching relay that results in a resistor being connected in series with dipped lights when ignition and sidelights are switched on. This safety feature as used on some vehicles – but not all.
Entry link: Dim-dip relay


An electronic one way valve with polarity bias manufactured from a semiconductor material.
Entry link: Diode

Diode Pack

A collection of diodes that act as a rectifier. A minimum of six diodes in the pack are needed for a three phase alternator.
Entry link: Diode Pack

Dip Switch

A switch used to select main beam or dipped beam headlights. Sometimes called a dimmer switch.
Entry link: Dip Switch

Dipped Beam

The lower of the two headlamp beams, dipped to avoid blinding the drivers of oncoming vehicles.
Entry link: Dipped Beam


To apply paint to an article by immersing it in a container of the paint and then withdrawing the article and allowing the excess paint to drain from the part. Particularly useful for small parts, such as nuts, bolts, brackets, etc.
Entry link: Dipping


A stick used to dip in a fluid and check its level!
Entry link: Dipstick

Direct Injection

Diesel engine design where fuel is injected directly into the cylinder.
Entry link: Direct Injection

Dirt Nibs

Small specks of foreign material in a dried paint film. They can be usually be removed by careful sanding and polishing.
Entry link: Dirt Nibs


Distributorless ignition system that uses an ignition coil or coils directly connected to the spark plugs. The ignition is triggered by the ignition module on signals from the ECM (Engine control module).
Entry link: DIS

Disc Brake

Brake in which external friction pads are brought to bear on the faces of a rotor or disc, usually by the clamping action of a caliper.
Entry link: Disc Brake

Disc Sander

Power sanding tool used for grinding, sanding, and rough polishing of repaired metal areas.
Entry link: Disc Sander

Discard Dimension

The lowest safe value for a component before it needs to be replaced. Used for brake components such as drums and rotors.
Entry link: Discard Dimension

Discharge Time

Refers usually to how long a capacitor will take to release all its stored energy. It can be calculated by multiplying the capacitance by resistance and by five (t = 5CR).
Entry link: Discharge Time


Change in colour of paint due to chalking, dirt collection, fading, darkening or tonal changes.
Entry link: Discoloration


Unfair or unequal treatment of a person due to their age, sex, disability, race, religion etc.
Entry link: Discriminatory


The act of removing a connection between two gears of through a clutch.
Entry link: Disengagement

Disk Drives

The primary data storage device used by computers. It stores and retrieves data.
Entry link: Disk Drives

Dispersion Coatings

A type of paint in which the binder molecules are present as colloidal particles. Characterized by a higher percent sprayable solids than is possible with solution-bases paints.
Entry link: Dispersion Coatings


The swept volume of a cylinder between the top and bottom positions of the top of a piston.
Entry link: Displacement

Displacer Unit

A hydraulic suspension component that contains gas under pressure and a fluid.
Entry link: Displacer Unit


Metallic particles from the basecoat surface in the clearcoat. If severe, the effect can alter the tone and exaggerate the metallic appearance.
Entry link: Dissolution


Purified by evaporation and condensation.
Entry link: Distilled


Distillation is a method of separating mixtures based on differences in their boiling points in a liquid mixture.
Entry link: Distilling

Distinctness of Image

A measurement of the accuracy of a reflection in a paint film, which assists the painter in determining the quality of the surface gloss.
Entry link: Distinctness of Image


A component in the ignition system that houses the primary circuit switching device and the secondary circuit distribution components.
Entry link: Distributor

Diverter Valve

Used on air injection systems to control the air feed according to the engine running conditions. Also known as a 'dump valve'.
Entry link: Diverter Valve


A digital circuit that, for example, reacts to only every second input hence dividing it in two.
Entry link: Divider


Data link connector for connecting a diagnostic tool to a vehicle's electronic systems.
Entry link: DLC

Dog Clutch

Pegs or similar used to transfer drive rotation from one component to another.
Entry link: Dog Clutch

Dog Drives

Pegs or similar used to transfer drive rotation from one component to another.
Entry link: Dog Drives


Dual overhead camshaft. Sometimes double overhead camshaft.
Entry link: DOHC

Donut Coupling

A rubber universal joint shaped like a donut.
Entry link: Donut Coupling

Double-Cardan Universal Joint

Two Hooke's or Cardan type universal joints close coupled to increase the effective angle of turn before inducing vibration.
Entry link: Double-Cardan Universal Joint


A technique that was necessary before the use of synchromesh mechanisms. During a gear change the clutch is lifted as the gear mechanism moves to neutral, the engine is revved (if changing down), the clutch is now depressed and the new gear selected.
Entry link: Double-declutch


A locating pin between two mating components. Can be solid or hollow.
Entry link: Dowel

Down Draft

A carburettor where the choke tube (venturi) is fitted vertically.
Entry link: Down Draft

Downdraft Booth

A spray booth in which the air movement is from the ceiling (input air) through the floor (extracted air).
Entry link: Downdraft Booth

Downshift Valve

Automatic transmission valve to give a downshift under specific drive conditions.
Entry link: Downshift Valve


Diesel Particulate Filter
Entry link: DPF

Drag Link

Steering linkage between the steering box drop arm (Pitman arm) and the drag arm on the steering swivel.
Entry link: Drag Link

Drain Plug

Removable plug used to let fluid out (engine oil for example).
Entry link: Drain Plug

Drain Tap

A simple valve used to allow a fluid to be removed.
Entry link: Drain Tap

Drain Tube

A tube used to, for example, remove moisture from an air conditioning evaporator.
Entry link: Drain Tube


A chemical which, when added to an enamel, paint, varnish, or oil, hastens the drying or hardening of the film through evaporation.
Entry link: Drier

Drive Axle

An axle that transmits a drive to the wheels. Also known as a live axle.
Entry link: Drive Axle

Drive Belt

Traditionally called the fan belt. A Vee or multi-vee belt to take drive from the engine to auxiliary components such as an alternator or water pump.
Entry link: Drive Belt

Drive Flange

A flange that is used to transmit drive from one component to another. The flange on the end of a propshaft is a good example.
Entry link: Drive Flange

Drive Gear

A toothed wheel to pass drive to another toothed wheel.
Entry link: Drive Gear

Drive Joints

General term used to describe any joint in a drive system such as a CV or universal joint.
Entry link: Drive Joints

Drive Line

Rotary shafts carrying drive to the wheels.
Entry link: Drive Line

Drive Motor

A motor that supplies a driving force. Term usually refers to an electric motor.
Entry link: Drive Motor

Drive Pinion

A small gear that drives another gear.
Entry link: Drive Pinion

Drive Plate

A plate that takes the place of the flywheel on an engine such as to transfer drive to a torque converter.
Entry link: Drive Plate

Drive Pulleys

Pulleys that transfer drive from one shaft to another.
Entry link: Drive Pulleys

Drive Ratios

Ratio between gears. For example 2:1 or 1.3:1.
Entry link: Drive Ratios

Drive Shafts

Open shafts carrying the drive from the final drive to the driven wheels.
Entry link: Drive Shafts


Transmission components in the line between the engine and wheels.
Entry link: Driveline

Driveline Wind-up

Description of how a vehicle in four-wheel drive (with no centre differential) can build up spring tension in its transmission components. This is because the front wheels may rotate at a slightly different speed to the rear wheels.
Entry link: Driveline Wind-up

Driven Plane

The plane (like a flat sheet) through which the drive operates.
Entry link: Driven Plane

Driven Plate

The clutch disc that is driven by the pressure plate.
Entry link: Driven Plate


Open shafts carrying the drive from the final drive to the driven wheels.
Entry link: Driveshafts

Driving Beam

The upper of the two headlamp beams. Also main beam and upper beam.
Entry link: Driving Beam

Driving Thrust

Forces generated by the engine and transmission.
Entry link: Driving Thrust

Drop Arm

The output arm on a steering gearbox. Also known as a Pitman arm.
Entry link: Drop Arm

Drop-Coat (Finesse coat)

A paint application method recommended on many Technical Data Sheets to eliminate patchy finishes in metallic and pearlescent basecoats. The atomising air pressure is reduced and the gun is held further from the surface. Providing the spray gun is then moved across the surface at a uniform speed, angle and distance, this technique should result in better orientation of the metallic and mica particles.
Entry link: Drop-Coat (Finesse coat)

Dropping Resistors

Resistors used to reduce voltage to a component.
Entry link: Dropping Resistors

Drum Brake

Brake in which friction blocks or brake shoes lined with friction material are brought to bear on the periphery of a drum or cylinder. In most vehicle applications the shoes are brought into contact with the inner periphery of the drum.
Entry link: Drum Brake

Dry Clutch

A friction clutch that runs in an open housing. As distinct from a wet clutch that runs in an oil bath.
Entry link: Dry Clutch

Dry Coat

A paint having a very low solvent content which produces a gritty film appearance.
Entry link: Dry Coat

Dry Film Thickness

The resultant film thickness of a coating after it has reached its final state of drying or curing. Measured in microns.
Entry link: Dry Film Thickness

Dry Liner/Dry Sleeve

(US: dry sleeve) Hard metal engine cylinder liner or insert that is not exposed to contact with cooling water.
Entry link: Dry Liner/Dry Sleeve

Dry Sanding

A method of abrading the surface by hand or machine without the aid of any water or other lubricant.
Entry link: Dry Sanding

Dry Spray

Sprayed paint which loses so much solvent in the air that it becomes too dry to flow out over the surface. This normally occurs when the chosen thinners is too fast for the atmospheric or application conditions.
Entry link: Dry Spray

Dry Sump (Oil Pan)

An engine lubrication system where the reservoir of lubricating oil is held in an oil tank. The sump (oil pan) below the engine is scavenged with a separate pump for return to the oil tank. As distinct from a wet sump (oil pan) where the reservoir of lubricating oil is kept in an oil pan below the engine.
Entry link: Dry Sump (Oil Pan)


The change from a liquid to a solid which takes place after a paint is deposited on a surface. This involves both the evaporation of the solvents and any chemical changes that may occur.
Entry link: Drying

Drying Oil

A liquid that will change to a solid under normal atmospheric conditions when spread out in a thin film.
Entry link: Drying Oil


Direct shift gearbox
Entry link: DSG


Diagnostic Trouble Code
Entry link: DTC


Dial Test Indicator.
Entry link: DTI

Dual Bed Converter

A three way catalytic converter with one stage coated with platinum and palladium and the other with platinum and rhodium. Converts HC and CO to H and CO2 and NOX to N and O.
Entry link: Dual Bed Converter

Dual Circuit Brake System

A brake system that has two independent hydraulic circuits so that one continues to act if the other fails. The split of dual circuits can be front and rear, diagonal, split front and one rear, and two complete circuits.
Entry link: Dual Circuit Brake System

Dual mass flywheel

A dual-mass flywheel is used to isolate torsional crankshaft spikes created by diesel engines during the power stroke. Dual mass flywheels separate the mass of the flywheel between the engine and the transmission. This eliminates damage to the transmission components.
Entry link: Dual mass flywheel

Dual Master Cylinder

A brake master cylinder with two separate chambers for a dual circuit hydraulic system.
Entry link: Dual Master Cylinder


Pipe, tube or trunking.
Entry link: Duct


The property of a material that allows it to be drawn into wires.
Entry link: Ductility


Large pipes or similar. Usually refers to the air intake system components.
Entry link: Ducting

Dump Valve

See diverter valve.
Entry link: Dump Valve


Refers to the retention of gloss and performance properties in a paint film during prolonged use or exposure to sunlight and other atmospheric conditions.
Entry link: Durability

Dust Contamination

Contamination due to visible dust particles of various sizes and forms which are embedded or form raised spots in the paint coating.
Entry link: Dust Contamination


Condition when a new paint film has dried sufficiently that it will no longer allow dust to penetrate and stick to the finish.
Entry link: Dust-Free

Duty Cycle

The percentage length of time that an actuator or solenoid is energised by an electronic control unit. Refers to the pulse width.
Entry link: Duty Cycle


Digital Volt Ohm Meter
Entry link: DVOM

Dwell Angle

The angle of distributor cam rotation when the contact breaker points are closed.
Entry link: Dwell Angle

Dwell Meter

Measures the dwell angle.
Entry link: Dwell Meter

Dwell Period

The angle of distributor cam rotation when the contact breaker points are closed. This term is used when the dwell angle is not a fixed value. Used for electronic ignition systems.
Entry link: Dwell Period


A term that indicates components that are in motion. The opposite of static.
Entry link: Dynamic


Machine converting mechanical energy into electrical energy. DC.
Entry link: Dynamo


A measuring device for engine power output. A brake dynamometer measures the output at the engine flywheel to give the term brake horse power (bhp). A rolling road dynamometer measures the output at the vehicle wheels and is used for test and diagnostic purposes.
Entry link: Dynamometer


E.C. (E)

European Commission (Executive).
Entry link: E.C. (E)


Electronic Control Unit."
Entry link: E.C.U


Electronic Control Unit.
Entry link: E.C.U.


Electro Motive Force.
Entry link: E.M.F.(emf.)


Electrically Erasable Programmable Read Only Memory
Entry link: E2PROM


Electronic Air Control Valve
Entry link: EACV

Early Fuel Evaporation

Early fuel evaporation system using a heater element below a carburettor to heat the intake air and improve atomisation at cold engine speeds. Improves driveability and reduces harmful exhaust emissions.
Entry link: Early Fuel Evaporation

Earth (Ground)

The electrical termination for components connected into a vehicle direct current earth return circuit. On mains electricity a safety route for an electrical short circuit used as a means of protecting people or electrical components from electrical overload.(Ground - US term)
Entry link: Earth (Ground)

Earth (Ground) Cable

The battery cable connecting the return side of a vehicle circuit to a terminal on the battery where a ground return circuit is used. (Ground - US term).
Entry link: Earth (Ground) Cable

Earth Switching

Used to describe a circuit where the switch breaks the earth side of the circuit instead of the supply side.
Entry link: Earth Switching

Earth Switcing

See Earth Switching!
Entry link: Earth Switcing


Electronically controlled automatic transmission.
Entry link: EATX


Electronic Brake Control Module
Entry link: EBCM


Electronic Body Module
Entry link: EBM


Electronic Control Assembly
Entry link: ECA


Electronic Control of Automatic Transmission
Entry link: ECAT


Off centre. Usually refers to a rotating component with the operational part rotating about the central axis of the shaft. An example is a round cam offset from the shaft axis.
Entry link: Eccentric


Engine control module. The electronic control module for engine management systems.
Entry link: ECM


Engine coolant temperature sensor or sender.
Entry link: ECT


Electronic Control Unit.
Entry link: ECU


Electronic Diesel Control.
Entry link: EDC


Painting technique where full panels are sprayed without blending into masked off adjacent panelwork, or where panels are removed from the vehicle to be painted
Entry link: Edge-to-edge


Electronic distributor or distributorless ignition system.
Entry link: EDIS


Explanation Demonstration Participation – a reminder of a good way to teach something practical to somebody.
Entry link: EDP


Electronic engine control module.
Entry link: EEC


Electronically Erasable Programmable Read Only Memory
Entry link: EEPROM


Electronic Fuel Control
Entry link: EFC


Electronic Fuel Control Assembly
Entry link: EFCA


Early fuel evaporation system using a heater element below a carburettor to heat the intake air and improve atomisation at cold engine speeds. Improves driveability and reduces harmful exhaust emissions.
Entry link: EFE


A measure of effectiveness given as a ratio, percentage or decimal value (co-efficient) based on actual and possible performance.
Entry link: Efficiency

Efficiency (energy)

Energy conversion efficiency is the ratio between the useful output of an energy conversion machine and the input, in energy terms. The useful output may be electric power, mechanical work, or heat.
Entry link: Efficiency (energy)


To produce work without wasting time and energy.
Entry link: Efficient


A force or action that tries to achieve something.
Entry link: Effort


Electronic fuel injection using sensors, an electronic control unit and fuel injectors to spray fuel into a central throttle body or the inlet ports. Provides very close control of fuel mixture under all operating conditions.
Entry link: EFI


Exhaust Gas Oxygen Sensor. Also HEGO - Heated Exhaust Gas Oxygen Sensor, EOS Exhaust Oxygen Sensor and Lambda sensor. Provides information to the fuel system ECU on the oxygen content in the exhaust gas.
Entry link: EGO


Exhaust gas recirculation. An emission control system that uses an exhaust gas feed into the intake air stream to reduce the mass of oxygen in the air charge and limit the formation of harmful oxides.
Entry link: EGR


EGR Valve Position Sensor
Entry link: EGRPS


EGR Temperature
Entry link: EGRT


Electronic Ignition
Entry link: EI

Elastic Limit

Amount of deflection in a spring that can be tolerated before permanent deformation occurs.
Entry link: Elastic Limit


The property of materials that can deform and return to their original shape without permanent deformation.
Entry link: Elasticity

Electric Field

Area round an electric charge in which an electric force is exerted.
Entry link: Electric Field

Electrical Energy

The potential of electricity to do work.
Entry link: Electrical Energy

Electro Motive Force (e.m.f.)

Voltage or pressure in a circuit.
Entry link: Electro Motive Force (e.m.f.)

Electro Motive Force (emf.)

Electrical energy available to a circuit at the battery or generator.
Entry link: Electro Motive Force (emf.)

Electro Plating

Coating with chromium, silver, etc. by electrolysis.
Entry link: Electro Plating

Electro-coating (Electrophoretic coating)

Electro-coating is an organic coating method that uses electrical current to deposit paint onto vehicle bodies, part, or other assembled products.
Entry link: Electro-coating (Electrophoretic coating)


Usually a metallic conductor which conducts electricity into a liquid, a gas, a vacuum or on to the surface of a solid.
Entry link: Electrode


A method by which paint is applied electrically by immersing electrodes and the work to be painted in a water-based paint and applying a direct electrical current to them.
Entry link: Electrodeposition


A combination of electrical and hydraulic control systems.
Entry link: Electrohydraulic


Electroluminescence (EL) is an optical and electrical phenomenon in which a material emits light in response to an electric current passed through it, or to a strong electric field. It is used on in car entertainment systems and instruments on some vehicles.
Entry link: Electroluminescence


A liquid that conducts electricity. Battery acid is a good example.
Entry link: Electrolyte


A magnet formed by a soft iron core and an electrical winding about the core. Becomes a magnet when an electrical current flows through the windings.
Entry link: Electromagnet


See electromagnet.
Entry link: Electromagnetic

Electromagnetic Oscillation

Changes from one value to another in a circuit. Usually produces a sine wave output or similar.
Entry link: Electromagnetic Oscillation

Electromagnetic Solenoid

A solenoid (coil of wire) that is used to operate an actuator such as a fuel injection.
Entry link: Electromagnetic Solenoid

Electromagnetic Valve

A valve that is operated by a coil of wire, which becomes magnetic when switched on.
Entry link: Electromagnetic Valve


Electrons form the outer shell layers of atoms and orbit the protons and neutrons in the nucleus. The electrons have negative polarity and are electrically negative in opposition to the positive charge of the protons.
Entry link: Electron

Electron Shell

Term used to describe the orbit of electrons round a nucleus.
Entry link: Electron Shell


Electrical systems operated or controlled by semi-conductor devices.
Entry link: Electronic

Electronic Control

System usually based round an electronic control unit where the operation of the system is pre-programmed.
Entry link: Electronic Control

Electronic Ignition

Petrol ignition system in which switching semi-conductors make and break the low tension circuit.
Entry link: Electronic Ignition


Describes the electrical state of something as in static (not flowing) electricity.
Entry link: Electrostatic


The basic form of a material.
Entry link: Element


Electronic Mail. Messages sent from one person to another electronically via a computer.
Entry link: Email


Electromagnetic compatibility. EMC requirements stipulate that a device shall not cause interference within itself or in other devices, or be susceptible to interference from other devices.
Entry link: EMC

Emergency Brake

A legal requirement for all vehicles provided by a split hydraulic circuit or a mechanically operated parking brake.
Entry link: Emergency Brake

Emery Paper

Carborundum grit on a backing sheet.
Entry link: Emery Paper


Electromagnetic Interference
Entry link: EMI

Emission Control

Systems on the vehicle to control (limit) toxic emission.
Entry link: Emission Control


Systems on the vehicle to control (limit) toxic emission.
Entry link: Emission-control


Terminal of a transistor that becomes conductive when the base is energised.
Entry link: Emitter


A way of expressing emotions in online communication. E.g., :-)
Entry link: Emoticons


Electronic Module Retard
Entry link: EMR


A suspension of fine particles in a liquid. The dispersed particles may be binder, pigments, or other ingredients.
Entry link: Emulsion

Emulsion Tube

Combined main and compensating jet tubes in a carburettor with provision for drawing air into the fuel flow to create an emulsion at higher engine speeds, thus preventing over-richness and improving fuel distribution.
Entry link: Emulsion Tube


EN European Standard e.g. BS EN 50342-2:2007 relates to: Lead-acid starter batteries and is a combined British and European standard (Dimensions of batteries and marking of terminals)
Entry link: EN


A paint type which forms a film by absorbing oxygen during curing. Characterised by slow drying and having a highly glossy, finished appearance without polishing.
Entry link: Enamel

End Float

Longitudinal play in shaft, intentional or otherwise.
Entry link: End Float

End Play

Alternative term for end float. Longitudinal play in shaft, intentional or otherwise.
Entry link: End Play


An ability to perform work. SI unit is the 'Joule'.
Entry link: Energy


The act of making a connection between two gears of through a clutch.
Entry link: Engagement

Engaging Pin

A simple pin used to make a drive connection.
Entry link: Engaging Pin

Engaging Plunger

General term to describe a plunger that engages something! Often part of a gearbox.
Entry link: Engaging Plunger

Engine Analyser

Complex test equipment used to check a variety of engine operating functions and conditions. An oscilloscope is usually included.
Entry link: Engine Analyser

Engine Analyzer

Complex test equipment used to check a variety of engine operating functions and conditions. An oscilloscope is usually included.
Entry link: Engine Analyzer

Engine Block

Main part of the engine that contains the cylinders.
Entry link: Engine Block

Engine Compartment

The space under the bonnet!
Entry link: Engine Compartment

Engine Load

How hard the engine is having to work. For example, accelerating uphill creates a high load.
Entry link: Engine Load

Engine Management

General term used to describe the control of engine operating functions such as ignition and fuelling. Usually related to electronic control.
Entry link: Engine Management

Engine Map

A three dimensional map held in a microprocessor that provides an optimum set of values for the control of ignition timing, ignition dwell period and fuel quantities for all engine operating conditions.
Entry link: Engine Map

Engine Speed Sensor

Provides information on engine speed to engine management systems (transducer).
Entry link: Engine Speed Sensor

Engine Support Beams

A bar that is used to support an engine, for example, after the transmission has been removed.
Entry link: Engine Support Beams

Engine Temp. Sensor

Engine temperature sender unit for temperature gauge and engine management systems (thermistor).
Entry link: Engine Temp. Sensor

Engine Torque

The amount of turning force produced by an engine. Usually quoted at a set speed.
Entry link: Engine Torque


Process of increasing the mixture strength / reducing the air fuel ratio.
Entry link: Enrichment


European Onboard Diagnostics
Entry link: EOBD


EOS Exhaust Oxygen Sensor. Provides information to the fuel system ECU on the oxygen content in the exhaust gas. Also EGO Exhaust Gas Oxygen Sensor, HEGO Heated Exhaust Gas Oxygen Sensor and Lambda sensor.
Entry link: EOS


Environmental Protection Agency
Entry link: EPA

Epicyclic Gear

See Epicyclical Gearing.
Entry link: Epicyclic Gear

Epicyclical Gearing

A gear system, consisting in basic form of an internally toothed annulus or ring gear and a central externally toothed sun wheel, with usually three or four planet wheels or gears meshing with the sun wheel and annulus. The planet wheels are often carried as a unit on a planet carrier or spider. Holding the rotation of the planet carrier, annulus or sun wheel will provide a transmission ratio between the two remaining elements. Planetary gear sets can be coupled to increase the available number of ratios.
Entry link: Epicyclical Gearing


An epitrochoid is a shape traced by a point attached to a circle of radius r rolling around the outside of a fixed circle of radius R, where the point is a distance d from the centre of the exterior circle. It is the shape of the cylinder in a Wankel engine.
Entry link: Epitrochoid


EGR Valve Position Sensor
Entry link: EPOS


A type of paint, adhesive or plastic noted for high mechanical strength, good adhesion and excellent chemical resistance.
Entry link: Epoxy


Erasable Programmable Read Only Memory.
Entry link: EPROM


Exhaust Electronic Pressure Transducer.
Entry link: EPT


Electronic Spark Control
Entry link: ESC


Electronic Spark Timing
Entry link: EST


A type of organic compound used as active solvents.
Entry link: Ester


An opinion or judgement.
Entry link: Estimate


Emergency Testing – the process by which testing may continue when the computerised system is not available due to a wide scale failure affecting a significant number of VTSs.

Entry link: ET

Etch Primer

Primer with an acid (usually Phosphoric) content. The purpose of the Etch primer in a coating system is to improve the adhesion and corrosion performance of the undercoat system. Their use is recommended when working with ferrous substrates, and essential on non-ferrous substrates
Entry link: Etch Primer


The process of a strong chemical cutting into unprotected parts of a metal.
Entry link: Etching


Ethyl-alcohol produced from starches and sugar plants and used as an octane enhancer.
Entry link: Ethanol

Ethyl Acetate

A fast evaporating ester solvent.
Entry link: Ethyl Acetate

Ethyl Alcohol

An inexpensive, fast evaporating solvent or diluent.
Entry link: Ethyl Alcohol

Ethylene Glycol

Anti-freeze. Chemical used to lower freezing point of coolant.
Entry link: Ethylene Glycol


The European Union (EU) is an economic and political union of 27 (as at 2010) member states, located primarily in Europe. Committed to regional integration, the EU was established by the Treaty of Maastricht on 1 November 1993.
Entry link: EU

Evaluation Circuit

An electronic circuit used to decide a course of action.
Entry link: Evaluation Circuit


Emission control system that uses a charcoal canister to prevent fuel tank vapours from venting to the atmosphere. The vapours are drawn into the engine during specific running conditions to purge the canister.
Entry link: EVAP


The change from liquid to a gas. When solvents leave a wet paint film, they usually do so by evaporation.
Entry link: Evaporation

Evaporation Rate

The speed at which any liquid evaporates.
Entry link: Evaporation Rate

Evaporative Canister

A canister usually containing charcoal that prevents emissions from the fuel tank due to evaporation.
Entry link: Evaporative Canister


A radiator in the air conditioning system fitted in the heater and A/C housing. The refrigerant passes through the pipes in the evaporator and vaporises to absorb heat and therefore cool the air stream flowing into the vehicle passenger compartment.
Entry link: Evaporator


This is what a candidates needs to produce to prove they have the skills required.
Entry link: Evidence


EGR Valve Position Sensor
Entry link: EVP


Electronic vacuum regulator solenoid on EGR system.
Entry link: EVR

Excess Pressure Valve

A pressure relief valve that opens if pressure exceeds a set value. Often for safety reasons.
Entry link: Excess Pressure Valve

Exhaust Blow-by

Gases from the exhaust bypassing a component, for example, the piston rings or a valve in a turbocharger.
Entry link: Exhaust Blow-by

Exhaust Emissions

Substances vented into the atmosphere from an exhaust system.
Entry link: Exhaust Emissions

Exhaust Gas Analyser

An instrument for measuring the constituent gases in the exhaust.
Entry link: Exhaust Gas Analyser

Exhaust Gas Analyzer

See Exhaust Gas Analyser.
Entry link: Exhaust Gas Analyzer

Exhaust Gas Recirculation

An emission control system that uses an exhaust gas feed into the intake air stream to reduce the mass of oxygen in the air charge and limit the formation of harmful oxides.
Entry link: Exhaust Gas Recirculation

Exhaust Manifold

Heat resisting ducting that connects the exhaust ports of an engine to an exhaust pipe.
Entry link: Exhaust Manifold

Exhaust Ports

Outlets in the cylinder head for the exhaust after the valve opens. In a two-stroke engine the ports are in the side of the cylinder.
Entry link: Exhaust Ports

Exhaust Stroke

The last stroke of the four stroke cycle when the burnt gases are expelled to the atmosphere.
Entry link: Exhaust Stroke


An increase in size. For example, when a metal rod is heated it increases in length and diameter. Opposite of contraction.
Entry link: Expansion

Expansion Box

Open muffler in the exhaust system to reduce the noise.
Entry link: Expansion Box

Extender Pigment

An inert, usually colourless and semi-transparent pigment used in paints to fortify and lower the price of pigment systems.
Entry link: Extender Pigment

Extension Housing

Usually describes an extra housing on the rear of a transmission gearbox.
Entry link: Extension Housing

External assessment

A test set externally to check portfolio evidence.
Entry link: External assessment

External Customer

One outside of an organisation.
Entry link: External Customer



Entry link: F


Fast CAN
Entry link: F-CAN


Front wheel drive."
Entry link: F.W.D.


The colour perceived by the brain when a painted surface is viewed from an angle of 90° - that being the angle at which the greatest amount of light reflection will occur
Entry link: Face-tone

Factory-applied Paint

Paint applied to a vehicle at the factory of the original equipment manufacturer (OEM). Factory-applied paint is normally cured by baking.
Entry link: Factory-applied Paint


The gradual loss of colour or gloss of a paint film due to a chemical or physical change, usually due to natural ageing or exposure to harmful environmental conditions
Entry link: Fading

Fail Safe

A device or feature that prevents total failure in the event of a fault occurring.
Entry link: Fail Safe


The process by which testing may continue when the computerised system is not available at a VTS, for example, following the breakdown of the VTS device.

Entry link: Fallback

Fallback Review

The process by which test data recorded while testing under Fallback is subsequently confirmed on the MOT computer database.

Entry link: Fallback Review

Fan (fan width)

The spray pattern of paint as it is emitted from a spray gun. Most spray guns have adjustments that can alter the fan width from a small round pattern to an elongated elliptical pattern.
Entry link: Fan (fan width)

Fan Cowl

A protective shield around a fan.
Entry link: Fan Cowl


The unit of capacitance.
Entry link: Farad

Fascia Panel

The panel inside the vehicle below the front windscreen. It carries the instruments, heater ducts and accessories.
Entry link: Fascia Panel

Fast Charge

Rapid charge for a battery. 5 times the Ah capacity for about an hour is the recommended maximum.
Entry link: Fast Charge

Fast Idle

The cold engine running speed achieved by a stepped cam on the throttle linkage or by an air bleed valve.
Entry link: Fast Idle


Failure in a material due to excessive and repeated loading usually of an intermittent nature.
Entry link: Fatigue


The cause of a problem that results in symptoms
Entry link: Fault

Fault Code

A code generated in and output from an ECU. Used for diagnostics.
Entry link: Fault Code


In engineering, fault-tolerant design, also known as fail-safe design, is a design that enables a system to continue operation, possibly at a reduced level, rather than failing completely, when some part of the system fails.
Entry link: Fault-tolerant


Feedback Carburettor System
Entry link: FBC


Feedback Carburettor Actuator
Entry link: FBCA


Fuel Control Solenoid
Entry link: FCS


Fuel Deceleration Valve
Entry link: FDC

Feather-edge Splitting

Fractures or cracks along the feather-edge which occur during drying or shortly after the topcoat has been applied over primer-surfacer. This problem occurs due to poor preparation, use of excessively fast solvents in primer, improper flash-off time and/or very aggressive solvents in topcoat.
Entry link: Feather-edge Splitting


Tapering a paint edge from substrate to topcoat or between layers of paint material by sanding. If feather-edging has been carried out efficiently, it should not be possible to feel the edges with the finger tips.
Entry link: Feather-edging


Term used to describe the way a tyre wears when the tracking is set incorrectly. The tread scuffs up like feathers.
Entry link: Feathering

Feed (leather)

The process of treating leather with soaps and creams to improves its lifespan and appearance.
Entry link: Feed (leather)

Feed Cable

The main supply wire to a component.
Entry link: Feed Cable


A feature used in electronic control systems to monitor performance by the use of a sensor downstream of an actuator. An example is an exhaust oxygen sensor monitoring the fuel injection quantities.
Entry link: Feedback

Feedback Resistor

A variable resistor used to indicate position of a moving component.
Entry link: Feedback Resistor

Feeler Gauge

Set of accurate blades used to set or measure small gaps (valve clearances for example).
Entry link: Feeler Gauge


These are chemical compounds, ceramic with iron oxide as their main components. Many of them are magnetic materials and they are used to make permanent magnets, ferrite cores for transformers, and in various other high tech applications.
Entry link: Ferrites


Describes any metal composed of or containing iron, such as low-carbon steel, stainless steel, etc.
Entry link: Ferrous


Fuel Injection
Entry link: FI


Very fine fibres of glass that are supplied as reels of single fibres or spun together as woven matting. It is used in the manufacture of glass-reinforced vehicle bodies, panels, and for component parts and repairs on automobile bodies.
Entry link: Fibreglass

Field (Magnetic)

A magnetic flux about a permanent magnet or live electrical conductor.
Entry link: Field (Magnetic)

Field Circuit

An electrical control circuit for the field coils used to regulate the output from a generator.
Entry link: Field Circuit

Field Coil

An electrical winding round a magnet pole shoe that is used to create a magnetic field when an electrical current flows through the windings. The direction of current flow determines the polarity of the magnetic pole. Used in generators and electrical motors.
Entry link: Field Coil

Field Coil (Winding)

An electrical winding round a magnet pole shoe that is used to create a magnetic field when an electrical current flows through the windings. The direction of current flow determines the polarity of the magnetic pole. Used in generators and electrical motors.
Entry link: Field Coil (Winding)

Filament (Bulb)

The tungsten element in a bulb that glows to produce light.
Entry link: Filament (Bulb)


The tungsten elements in a bulb that glow to produce light.
Entry link: Filaments

Filiform Corrosion (Spidering)

A paint defect caused by moisture ingress between the substrate and the paint film, e.g. via an untreated stone chip, that continues to travel in 'spidery' threads.
Entry link: Filiform Corrosion (Spidering)


Commonly, a heavily pigmented sprayed foundation paint used to fill imperfections and pores in a substrate. To avoid confusion with 'Body Filler', should be referred to as 'Primer-Filler' or 'High-Build Filler'
Entry link: Filler

Filler Neck

The connection into the fuel tank for refuelling.
Entry link: Filler Neck

Fillet Radius

A machined curve between two faces of a component. An example is the curve between a crankshaft web and journal.
Entry link: Fillet Radius


A very thin continuous sheet of material. Paint forms a film on the surface to which it is applied.
Entry link: Film

Film Thickness

The thickness or depth of a dry paint film is important. Thin films may appear to be the wrong colour due to their lower opacity, and may also have durability issues. Over-thick films are likely to crack in use. The thickness of paint films on iron or steel surfaces is easily determined with a magnetic gauge.
Entry link: Film Thickness

Film Thickness Gauge

A device used to measure the coating thickness on a substrate. Magnetic devices are used to measure the thickness of ferrous metals; whereas electronic devices are used on non-ferrous substrates.
Entry link: Film Thickness Gauge


A fine mesh or paper screen used to remove dirt and other contaminants from a liquid or gas (air).
Entry link: Filter

Final Drive

The gearing immediately before the driven wheels. It provides a split to each driven wheel with a final gear reduction for the transmission. Can also be used to turn the drive through 90° with the use of bevel gears.
Entry link: Final Drive

Finesse coat

See 'Drop coat'
Entry link: Finesse coat


A protective coating of paint; usually referring to the final appearance of the painted surface. Also, to apply a paint or paint system.
Entry link: Finish

Finishing Film

A fine graded abrasive disc for sanding top coat automotive paints before repainting or compounding.
Entry link: Finishing Film


Substantial structural panel of vehicle body in front of passenger compartment. Also known as a bulkhead.
Entry link: Firewall

Firing Order

The sequence for ignition of individual cylinders in an engine.
Entry link: Firing Order

Fish Eyes

A surface depression or crater in the wet paint film. Fish Eyes are caused by repulsion of the wet paint by a surface contaminant such as oil or silicone. The depression may or may not reveal the surface under the paint, depending on its depth or severity.
Entry link: Fish Eyes

Fish-Eye Eliminator

Additive used in paint to prevent the occurrence of fish eyes (craters/silicones) in a freshly painted surface - usually caused by the presence of contaminants such as wax polish.
Entry link: Fish-Eye Eliminator

Fixed Caliper

A disc brake caliper in which the two halves and pistons are made as a single unit attached to the axle assembly.
Entry link: Fixed Caliper

Fixed Choke Carburettor

A carburettor with a fixed diameter venturi (choke tube).
Entry link: Fixed Choke Carburettor

Fixed Venturi

A narrowed section in a carburettor - the size of which remains fixed.
Entry link: Fixed Venturi


A decorative pigment consisting of flat particles. Usually mica, aluminium or other bright metals, providing special colour effects to the final paint finish.
Entry link: Flake

Flake Orientation

The appearance of the metallic particles in a paint film during and after drying or curing. Selection of the correct flakes in the colour mixing formula and proper application will lead to good flake orientation and thus to good colour match and appearance.
Entry link: Flake Orientation


A serious paint defect characterised by the paint film lifting and eventually falling off of the substrate.
Entry link: Flaking

Flame Plug

Cold start device fitted in the inlet manifold on some direct injection diesel engines.
Entry link: Flame Plug

Flame Trap

Incorporated into the air cleaner unit to prevent the spread of fire caused by fuel igniting in the carburettor if blow back occurs.
Entry link: Flame Trap


Flat face to flat face butted fitting. Method used to secure exhaust system.
Entry link: Flange

Flange Bolts

Bolts that secure a flat face to flat face butted fitting.
Entry link: Flange Bolts

Flange Fitting

Flat face to flat face butted fitting. Method used to secure exhaust system.
Entry link: Flange Fitting

Flare Joint

A method of connecting pipes, particularly steel brake pipes, where the end of the pipe is deformed to give a concave or convex flare which is secured with a union nut.
Entry link: Flare Joint

Flash Rusting

A surface rust occurring from improper cleaning or exposing bare metal to the air and moisture for too long of a period.
Entry link: Flash Rusting


The first stage of paint drying where some of the solvent content evaporates. This typically dulls the surface from an exceedingly high gloss to a normal gloss or flat appearance.
Entry link: Flash-off

Flash-off Time

The time between paint application and consecutive coats.
Entry link: Flash-off Time


The temperature at which a liquid will give off a flammable vapour that would ignite when a spark is struck.
Entry link: Flashpoint

Flat (finish)

Lacking in gloss. (See Matting agent)
Entry link: Flat (finish)

Flat Seat Valve

A valve that operates by one part operating against a flat component to control flow.
Entry link: Flat Seat Valve

Flat Spot

A temporary drop in power that occurs at the point of initial acceleration when the throttle plate is opened. Occurs as a result of a rise in venturi pressure (drop in vacuum) and a resultant loss of fuel supply into the venturi. Remedied by the addition of an accelerator pump.
Entry link: Flat Spot

Flat-seat Valve

A valve that operates by one part operating against a flat component to control flow.
Entry link: Flat-seat Valve


The rubbing down of repaired or pre-painted surfaces with abrasives to achieve the desired shape, prepare the surface for painting or prior to polishing.
Entry link: Flatting

Flex Plate

The mounting plate for a torque converter where it is attached to the crankshaft. Fits in place of the flywheel.
Entry link: Flex Plate


Being able to accept change.
Entry link: Flexible

Flexible Additive

A substance added to paint to improve its performance characteristics, such as impact resistance, flexibility, and elasticity when applied to plastic or flexible substrates.
Entry link: Flexible Additive

Flexible Coupling

A rubber or fabric reinforced rubber coupling that is used to join two shafts. Usually incorporates two forks that act as a safety device in the event of failure of the rubber component.
Entry link: Flexible Coupling


Another word for bending.
Entry link: Flexing


The change in value, hue, and chroma of a metallic or pearl car finish when it is viewed from different angles.
Entry link: Flip


The colour perceived by the brain when a painted surface is viewed from an acute angle (i.e. less than 90°). - the more acute the angle, the less amount of light reflection occurs, giving an impression that the colour is darker
Entry link: Flip-tone


A longitudinal cut
Entry link: Flitch

Flitch Panel

Structural panel of vehicle body on sides of engine.
Entry link: Flitch Panel


A buoyant component used to indicate or control fluid levels. In a carburettor used with a needle valve to control the petrol level in the float chamber.
Entry link: Float

Float Chamber

Part of carburettor holding petrol at a controlled level.
Entry link: Float Chamber


The tendency of pigment particles in a wet paint film to separate from one another and concentrate in particular areas, resulting in a 'patchy' finish
Entry link: Floating

Floating Caliper

A disc brake caliper that has a fixed component attached to the axle assembly and a single piston and caliper that is 'floating' by sliding or pivoting on the fixed component.
Entry link: Floating Caliper


Clumping together of pigment particles within the wet paint.
Entry link: Flocculation


The tendency of pigment particles to rise to the surface during curing and produce a colour variation at the surface and a lack of uniformity in the colour appearance through the film.
Entry link: Flooding

Floppy Disk

A portable disk that stores 1.44Mb of information.
Entry link: Floppy Disk


The levelling characteristics of a wet paint film.
Entry link: Flow

Flow Meter

A sensor that determines flow of a fluid or gas.
Entry link: Flow Meter


Fluid Level Sensor
Entry link: FLS

Fluid Coupling

A drive coupling that uses a fluid to transmit drive. Also sometimes a viscous coupling.
Entry link: Fluid Coupling

Fluid Flywheel

A drive coupling that uses a fluid to transmit drive.
Entry link: Fluid Flywheel

Fluid Needle

The part of a spray gun that opens and closes the fluid passage in the fluid tip.
Entry link: Fluid Needle

Fluid Pump

A pump for moving or pressurising a fluid.
Entry link: Fluid Pump

Fluid Tip

Part of a spray gun that meters and directs the fluid stream.
Entry link: Fluid Tip


Weights that act on pivots and move outwards due to centrifugal force.
Entry link: Flyweights


(1) Component of the clutch. (2) Massive wheel or disc attached, for example, to the crankshaft of an engine, to store energy of rotation and smooth the output from the irregular firing of the cylinders. In many automotive engines, the flywheel incorporates the ring-gear and acts as one friction face of the clutch. (3) Maintains the momentum of the engine.
Entry link: Flywheel


Fuel Octane Adjustment.
Entry link: FO


A term used to describe the aeration of an oil.
Entry link: Foaming

Focal Length

The distance between the focal point and the reflector.
Entry link: Focal Length

Focal Point

The point within a reflector from where a light source produces parallel beams.
Entry link: Focal Point


To the point.
Entry link: Focussed

Follower (Cam)

The component in contact with the cam on a camshaft.
Entry link: Follower (Cam)

Foot Pound

Old unit of torque. Also pounds/feet. Torque is now given in the SI units of Newton metres (Nm).
Entry link: Foot Pound


When applied to tyres describes the area and shape of the part of the tyre in contact with the road.
Entry link: Footprint


Exerted to overcome a load.
Entry link: Force

Force Ratio

The comparison of the force applied to the force produced via some kind of machine or system.
Entry link: Force Ratio


A method of accelerating the drying of paint with the aid of heat.
Entry link: Force-Dry


A component forming process applied to hot metal with a hammer or die either by hand or machine. Also hot stamping.
Entry link: Forging


Part of the door latch mechanism, clutch or gearbox. Fits around another component to hold or move that component.
Entry link: Fork

Fossil fuel

This relates to any fuel made from hydrocarbon deposits such as coal, petroleum, natural gas and, to some extent, peat; these fuels are irreplaceable, and their burning generates the greenhouse gas carbon dioxide.
Entry link: Fossil fuel

Four Stroke Cycle

The conventional operating principle for the modern internal combustion engine consisting of the induction, compression, combustion/power and exhaust strokes.
Entry link: Four Stroke Cycle

Four Wheel Drive (4WD) (4x4)

Transmission system that uses all four wheels of a vehicle to provide a drive. This term is usually used on vehicles with selectable four wheel drive. The term AWD for all wheel drive is used for vehicles with permanent four wheel drive.
Entry link: Four Wheel Drive (4WD) (4x4)

Four Wheel Steering (4WS)

A steering system that applies turning movement to front and rear wheels. The rear wheel steer is initially opposite to the front wheels, neutral and then with the front wheels. This provides steering characteristics that aid manoeuvrability.
Entry link: Four Wheel Steering (4WS)

Four Wheel Steering 4WS

A steering system that applies turning movement to front and rear wheels. The rear wheel steer is initially opposite to the front wheels, neutral and then with the front wheels. This provides steering characteristics that aid manoeuvrability.
Entry link: Four Wheel Steering 4WS


Fuel Pump.
Entry link: FP


Fuel Pump Relay.
Entry link: FPR


A number of parts out of another number of parts.
Entry link: Fractions


This is an authorization to sell a company's goods or services in a particular place.
Entry link: Franchise

Free Electrons

The electrons in the valency shell of an atom that can link with and move on from other atoms. A material with free electron flow makes a good electrical or heat conductor.
Entry link: Free Electrons

Free Play

The amount of free movement in or between components that is not transmitted to the next component in the sequence. May also be referred to as 'backlash' in some applications such as when applied to gears.
Entry link: Free Play

Free Travel

The free play in a clutch linkage before it operates the clutch mechanism.
Entry link: Free Travel


The amount of free movement in or between components that is not transmitted to the next component in the sequence. May also be referred to as 'backlash' in some applications such as when applied to gears.
Entry link: Freeplay


Overrun of a one way clutch. Vehicle movement when the transmission is not engaged to the engine.
Entry link: Freewheeling


The number of oscillations per unit of time. Examples are a sound wave or alternating electrical current. The unit for frequency is the Hertz, which equals one oscillation per second.
Entry link: Frequency


Resistance a body encounters in moving over another.
Entry link: Friction

Friction Disc

Term used to refer to a clutch drive plate.
Entry link: Friction Disc

Friction Discs

Component of the clutch. The centre plate that is gripped between the flywheel and pressure plate to transmit a drive to the gearbox input shaft.
Entry link: Friction Discs

Friction Material

A material with consistent performance characteristics used to provide a rubbing surface for brake and clutch components.
Entry link: Friction Material

Friction Plate

Component of the clutch. The centre plate that is gripped between the flywheel and pressure plate to transmit a drive to the gearbox input shaft.
Entry link: Friction Plate

Front-end Solvent

A fast-evaporating solvent that leaves the paint very soon after application.
Entry link: Front-end Solvent


Fuel Temperature Sensor.
Entry link: FT

Foot Pound"
Entry link:

Fuel Distributor

The component in a mechanical injection system that controls and distributes the fuel.
Entry link: Fuel Distributor

Fuel Efficiency

Performance of engine/vehicle. Rate of fuel usage.
Entry link: Fuel Efficiency

Fuel Filter

A filter to remove contamination from fuel.
Entry link: Fuel Filter

Fuel Gauge Sender

Sensor, usually a variable resistor, which supplies information on fuel quantity in the tank.
Entry link: Fuel Gauge Sender

Fuel Injection

The injection of fuel under pressure into the intake air stream of petrol engines by the use of electrical solenoid valves in place of a carburettor.
Entry link: Fuel Injection

Fuel Line

The pipes and hoses that connect the fuel system components.
Entry link: Fuel Line

Fuel Pressure Regulator

In a fuel system the component that keeps the pressure across injectors constant. It consists of a valve, diaphragm and spring.
Entry link: Fuel Pressure Regulator

Fuel Rail

A tube or pipe used to supply fuel to electrical injectors. The quantity of fuel in the rail is relatively large so that the pressure remains constant when the injectors operate.
Entry link: Fuel Rail


A pivot for a lever. Usually a supporting point or shaft.
Entry link: Fulcrum

Fulcrum Ring

A ring on which clutch release fingers pivot.
Entry link: Fulcrum Ring

Full Flow Lubrication

An engine lubrication system where all of the oil flows through the oil filter before entering the engine oil galleries.
Entry link: Full Flow Lubrication

Full Load

Describes the engine condition when it is working as hard as it is able - for acceleration for example.
Entry link: Full Load

Full Load Enrichment

A device in a carburettor that provides additional fuel during full throttle and heavy load conditions.
Entry link: Full Load Enrichment

Full Wave Rectification

Alternating current converted to direct current by reverse flow of the negative bias so that it is added to the forward bias electrical flow. Modern rectifiers using a diode bridge achieve full wave rectification.
Entry link: Full Wave Rectification

Fully Floating Axle

An axle hub arrangement that carries the load on two bearings and therefore does not apply a shear or bending force on the axle shaft.
Entry link: Fully Floating Axle


A safety device in an electrical circuit that will burn and melt to break the circuit when an excess current is applied.
Entry link: Fuse

Fuse Box

A central termination block in a vehicle electrical system that carries the fuses.
Entry link: Fuse Box

Fuse Rating

The rated value of a fuse before failure due to an excess current load. The rating can be either a constant or a surge value and is given in amps. Fuses are usually colour coded and marked for the fuse rating.
Entry link: Fuse Rating

Fuzzy Logic

A digital control system that makes 'educated' guesses.
Entry link: Fuzzy Logic


Front-Wheel Drive
Entry link: FWD


G or g

Unit of force equivalent to the force of the Earth's gravity.
Entry link: G or g


A force on an object equivalent to the force applied by the Earth's gravity.
Entry link: G-force

G/C Clamp

A clamp (hand tool) shaped like a G/C.
Entry link: G/C Clamp


A rubber (or similar) boot used to cover working components. It is used to keep dirt out and in some cases lubrication in place. Also slang for alligator...
Entry link: Gaiter


Entry link: gal


See Main Gallery.
Entry link: Galleries


A protective process for steel sheet where a thin surface layer of zinc is applied by hot dipping the steel into a bath of molten zinc.
Entry link: Galvanize

Ganged Switch

An electrical switch that operates two or more circuits from one switching point.
Entry link: Ganged Switch


A fluid state of matter when the atoms are free. The least dense state of matter which can have three states, solid, liquid and gas.
Entry link: Gas

Gas Analyser

Electronic equipment that measures exhaust gas constituents.
Entry link: Gas Analyser

Gas Analyzer

See Gas Analyser.
Entry link: Gas Analyzer

Gas Turbine

A type of internal combustion that uses rotating blades in a compressor to provide charging of the combustion chamber. The output gas pressure is used to drive turbine blades which are connected by a shaft to drive the compressor and a transmission gearbox or in the case of aircraft jet engines to provide air propulsion.
Entry link: Gas Turbine


A material that is fitted between faces to take up the irregularity of the surface finishes and provide a gas or liquid seal.
Entry link: Gasket


A hydrocarbon fuel made up from carbon and hydrogen elements. Used as a fuel for internal combustion engines. Also petrol.
Entry link: Gasoline


The formation, in the can, of gaseous products in a coating material, due to the reaction between two or more constituents of the coating material or between the latter and the metal of the container. Characterised by a 'Pop' sound when opening paint containers
Entry link: Gassing


In transmission systems a device to guide a gear into any one position at any one time. In electronics a logic device for regulating electrical current flow according to input voltage levels.
Entry link: Gate


Governor Control Module.
Entry link: GCM


Gasoline direct injection. Petrol/Gasoline is injected directly into the combustion chamber under high pressure.
Entry link: GDi


A method of providing leverage. Toothed wheel that meshes with another toothed wheel.
Entry link: Gear

Gear Brake

Part of an automatic gearbox, the brake is often a band of friction material.
Entry link: Gear Brake

Gear Cluster

A series of fixed gears on one shaft. Used to provide gear selection by engagement with freely rotating gears on another shaft. The selection is made by locking the freely rotating gear to the shaft. This can be by the use of a sliding hub or a sliding gear splined to the output shaft.
Entry link: Gear Cluster

Gear Clutch

A clutch that connects or disconnects drive to a gear.
Entry link: Gear Clutch

Gear Cogs

Toothed wheels that mesh with other toothed wheels.
Entry link: Gear Cogs

Gear Lash

The clearance between the teeth of two meshing gears. Also known as backlash when applied to gears.
Entry link: Gear Lash

Gear Pump

An oil pump using two meshed gears to provide a positive pumping action. The teeth are of the two gears run in mesh. Where they come out of mesh a small chamber forms to allow oil to flow in, the oil is carried round the periphery of pump in the gear teeth and when the teeth come into mesh the chamber is reduced in size and the oil forced from the pump.
Entry link: Gear Pump

Gear Ratio

Ratio of angular velocities of pairs of meshing gears. Number of teeth on driven gear divided by number of teeth on driver gear.
Entry link: Gear Ratio

Gear Reduction

A gear drive that reduces the rotational speed of the output shaft below that of the input shaft.
Entry link: Gear Reduction

Gear Train

Two or more gears in mesh that transmit a drive through them.
Entry link: Gear Train


A housing containing gears to allow different ratios to be selected.
Entry link: Gearbox

Geared Distributor

A distributor driven by a gear from the engine.
Entry link: Geared Distributor


The mechanism for selecting gears in the transmission. Consists of the driver's gear lever, the linkage to the transmission gearbox, and the selectors in the gearbox.
Entry link: Gearshift


Governor Electronic Module.
Entry link: GEM


Entry link: GEN


Machine for converting mechanical energy into electrical energy.
Entry link: Generator


A common type or something that is used for a variety of tasks.
Entry link: Generic

Gerotor Pump

A type of positive displacement oil pump that uses two gears on eccentric axes. One gear is on a shaft inside another rotating in the housing. The pumping and carrying chambers are formed between the gear teeth.
Entry link: Gerotor Pump


Reflection from the sun or a light onto the computer screen making it difficult to see properly.
Entry link: Glare


A polish that is safe for use on fresh paints. Some glazes contain a mild abrasive that will remove minor surface imperfections. When a glaze with an abrasive is used, it should be followed by application of wax on cured paint or a hand glaze on fresh paint. A glaze also does not contain silicone.
Entry link: Glaze


Person who works with glass.
Entry link: Glazier


The ability of a surface to reflect light. Measured by determining the percentage of light reflected from a surface at certain angles.
Entry link: Gloss

Gloss Meter

An apparatus for measuring the gloss of paint film.
Entry link: Gloss Meter

Glow Plug

Cold start device for diesel engine. Fitted into the combustion chamber and heated by an electrical current so that the injected air and fuel is heated as an aid to ignition when the engine is cold.
Entry link: Glow Plug


Entry link: GND


Popular Search Engine.
Entry link: Google


A control device that limits the speed of a unit or controls or senses the operation of a unit. An example is the governor in a diesel injection pump which controls the engine speed.
Entry link: Governor

Governor Pressure

The control pressure in an automatic transmission that senses vehicle speed. It is applied to the hydraulic control unit or valve body to effect gear shifts in relation to vehicle speed.
Entry link: Governor Pressure

Governor Valve

The valve in an automatic transmission, which is fitted on the output shaft. The rotational speed acts on a spring-loaded valve to regulate pump pressure. The governor pressure acts on the gear shift control plunger in the valve body.
Entry link: Governor Valve


Grams Per Mile
Entry link: GPM


Global Positioning System: This is a navigational system involving satellites and computers that can determine the latitude and longitude of a receiver on Earth by computing the time difference for signals from different satellites to reach the receiver.
Entry link: GPS

Grab (Brake)

A braking condition where the brakes lock up when light pedal effort is applied. Caused by brake linings digging into the drum or disc on application. Usually cured by forming a chamfer on the leading edge of the lining.
Entry link: Grab (Brake)


Forming well written, easy to read sentences, paragraphs and documents with the use of punctuation (i.e., full stops, commas etc.).
Entry link: Grammar


A device that propels rocks at a painted substrate to measure the resistance the finish has to rock chips.
Entry link: Gravelometer


The attraction that all masses experience as a force towards the earth - or any other planet for that matter!
Entry link: Gravity

Gravity-feed Gun

A spray gun which has the paint container on the top of the gun, allowing the paint to flow into the fluid passage by gravity.
Entry link: Gravity-feed Gun


A thick sticky lubricant made from a variety of bases, usually derived from crude oils, and used for bearing and chassis lubrication.
Entry link: Grease

Greenhouse gases

Gases that are a natural part of the atmosphere. They absorb and re-radiate the sun's warmth, and maintain the Earth's surface temperature at a level necessary to support life.
Entry link: Greenhouse gases


Abrading painted or unpainted metal surfaces to remove paint/corrosion or prepare the area for filling.
Entry link: Grinding


Refers to the abrasive size used in flatting papers, discs, etc. and is classified using 'P' grades, e.g. P40, P120, P600 and so on. The larger the number, the finer the abrasive
Entry link: Grit


A paint product is said to be gritty when it contains large particles, from insufficient dispersion during mixing or when it contains large hard particles of foreign materials.
Entry link: Gritty


A blind grommet is a rubber insert fitted into a hole in a plate to blank off the plate. Other types are used to provide protection for cables or pipes that pass through a hole.
Entry link: Grommet

Groove (Tire)

A channel cut in the tread of a tire to facilitate the dispersal of road surface water.
Entry link: Groove (Tire)

Groove (Tyre)

(1) A channel cut in the tread of a tyre to facilitate the dispersal of road surface water. (2) The machined slot around the piston into which the rings are fitted.
Entry link: Groove (Tyre)

Ground (Earth)

The electrical termination for components connected into a vehicle direct current ground return circuit. On mains electricity a safety route for an electrical short circuit used as a means of protecting people or electrical components from electrical overload.
Entry link: Ground (Earth)

Ground (Earth) Cable

The battery cable connecting the return side of a vehicle circuit to a terminal on the battery where a ground return circuit is used.
Entry link: Ground (Earth) Cable

Ground Clearance

The dimension under a vehicle which clears any obstacles in the roadway.
Entry link: Ground Clearance

Ground Test

A test to make sure the earth or ground or chassis electrical connection is in good working order.
Entry link: Ground Test


A safety practice where two objects are interconnected with clamps and bare wire. This equalizes the electrical potential between the objects and helps prevent static sparks that could ignite flammable materials.
Entry link: Grounding

Gudgeon Pin

The piston pin that connects a piston to a connecting rod. Fitted at the little end of the connecting rod. Also wrist pin.
Entry link: Gudgeon Pin


Petroleum distillate formed during combustion particularly with poor fuel quality. The gum is deposited on cylinder walls and increases the tendency for glazing.
Entry link: Gum

Gun Body

The main part of the spray gun to which all other component parts are attached.
Entry link: Gun Body


Gross Vehicle Weight
Entry link: GVW



Health And Safety at Work Act 1974.(UK)"
Entry link: H.A.S.W.A


Entry link: H20

Half Shafts

Shafts by which power is transmitted from final drive to driven wheels in an enclosed axle.
Entry link: Half Shafts

Hall Generator

An electronic pulse generator using the Hall effect of a semiconductor to provide information to the ignition amplifier or ECU on engine position and speed.
Entry link: Hall Generator

Hall IC

Integrated circuit as part of a Hall sensor.
Entry link: Hall IC

Hall Sensor

An electronic pulse generator using the Hall effect of a semiconductor to provide information to the ignition amplifier or ECU on engine position and speed. Also used for sensing road speed etc.
Entry link: Hall Sensor


A description of a series of gases such as argon.
Entry link: Halogen


Hand operated parking brake usually with a mechanical linkage. Also forms the reserve or emergency brake on many vehicles.
Entry link: Handbrake

Handbrake Cable

A cable that operates the brakes when a lever is pulled.
Entry link: Handbrake Cable

Handbrake Linkage

Cables or rods used to operate the parking/handbrake.
Entry link: Handbrake Linkage

Hard Disk

A storage device that holds large amounts of data.
Entry link: Hard Disk


A chemical specifically designed to ensure cure of a paint finish, filler, stopper, resin or adhesive. Also, another name for an activator.
Entry link: Hardener


The physical components of a computer system.
Entry link: Hardware


A physical connection between two or more electrical devices.
Entry link: Hardwired

Harmonic Balancer

Rotating or oscillating engine balance shaft.
Entry link: Harmonic Balancer


The collection of vehicle cables wound together with an insulation tape. Also known as a 'wiring loom'.
Entry link: Harness


Risky. Potential to harm people or property.
Entry link: Hazardous


The development of a cloudy area in the paint film or in a clear liquid.
Entry link: Haze


(1) Hydrocarbon. (2) High compression.
Entry link: HC

Head Gasket

Seal between cylinder block and cylinder head.
Entry link: Head Gasket


Viewing a repaired/re-painted area from an angle that is perpendicular (at 90°) to the car.
Entry link: Head-on

Head-up Display

Projection of instruments onto the windscreen so that the road and the instruments can be seen at the same time by the driver.
Entry link: Head-up Display

Header Tank

The expansion tank at the top of a coolant radiator, which can be part of the radiator or a separate tank.
Entry link: Header Tank


Vehicle lighting that provides illumination of the road for the driver. Usually consists of switched main and dipped beams.
Entry link: Headlamp

Headway Sensor

A device usually fitted in the front grill of a vehicle that in conjunction with a transmitter senses distance in front of the vehicle. Often part of an active cruise control system.
Entry link: Headway Sensor


A form of energy in all materials that can be used to do work.
Entry link: Heat

Heat Exchanger

A device for transferring heat from one system or place to another.
Entry link: Heat Exchanger

Heat Range

Applies to spark plug construction where the rate of heat loss from the plug nose is controlled by the length of the insulation. Spark plugs are given a rating from hot to cold to classify the heat range and application. The plug tip temperature is controlled to keep the tip and electrodes clean.
Entry link: Heat Range

Heat Sink

A plate to which electronic components are attached to dissipate heat.
Entry link: Heat Sink

Heater Matrix

Small radiator used to exchange heat from the coolant to the vehicle cabin.
Entry link: Heater Matrix


Heated Exhaust Gas Oxygen Sensor. Also EGO Exhaust Gas Oxygen Sensor, EOS Exhaust Oxygen Sensor and Lambda sensor. Provides information to the fuel system ECU on the oxygen content in the exhaust gas.
Entry link: HEGO


High Energy Ignition. A distributor ignition system using electronic control of the coil secondary output.
Entry link: HEI

Helical Gear

A gear with teeth cut at an angle.
Entry link: Helical Gear

Helical Rotor

A turbine or compressor in a turbocharger often has vanes that are helically shaped.
Entry link: Helical Rotor

Helical Spring

Metal spring used in vehicle suspension. Also known as a coil spring.
Entry link: Helical Spring


A sphere is a perfectly round geometrical object in three-dimensional space, such as the shape of a round ball - a hemisphere is half a sphere
Entry link: Hemisphere


A fuel used in research tests as a comparison when determining the octane rating of fuels. Octane value of zero.
Entry link: Heptane


The number of oscillations per unit of time. The SI unit for frequency is the Hertz which equals one oscillation per second.
Entry link: Hertz


Short for hexagonal.
Entry link: Hex


Entry link: Hg

Hide Mallet

Soft hammer made of hide (leather). Plastic types are also used.
Entry link: Hide Mallet

Hiding or Hiding Power

(See 'Opacity')
Entry link: Hiding or Hiding Power

High Boilers

Solvents with boiling points above 100 degrees Celsius.
Entry link: High Boilers

High Lift Cam

A special cam profile used on performance engines to increase the opening size of a valve.
Entry link: High Lift Cam

High resistance

An unwanted resistance in a circuit that causes it to operate incorrectly.
Entry link: High resistance

High Solids

Paints are described as having high solids when they contain more than 50-60% solids. High solids paints have lower VOC's.
Entry link: High Solids

High Tension

The term used for the high voltage in the secondary circuit of the ignition system.
Entry link: High Tension


Hall generator. A sensor using a Hall effect to provide signals to an ECU.
Entry link: HLG


Heated Oxygen Sensor
Entry link: HO2S


To lift something or a term used to describe a vehicle lift or ramp.
Entry link: Hoist

Hold-in Winding

A winding in a starter motor solenoid that holds the switch contacts together and the drive pinion in mesh during engine starting.
Entry link: Hold-in Winding


The ability of a surface to keep the topcoat from sinking in and causing a decrease in appearance or gloss.
Entry link: Holdout


Uniform in structure or composition throughout. This is usually used to refer to a fuel air mixture in a cylinder that is a 'perfect' mixture of fuel and air.
Entry link: Homogenous


A light grinding process applied to cylinder bores in preparation for the fitting of new pistons.
Entry link: Hone

Hooke's Joint

A drive shaft universal joint consisting of two yokes and a cross bearing. Also Cardan joint.
Entry link: Hooke's Joint

Horizontally Opposed

An engine configuration where cylinder pairs are fitted on opposite sides of the crankshaft. Sometimes referred to as 'Boxer' engines.
Entry link: Horizontally Opposed


A measure of power equivalent to 0.746 Kilowatts. Defined by a rate of doing work of 33,000 foot pounds per minute (550 foot pounds per second).
Entry link: Horsepower


Heated Oxygen Sensor.
Entry link: HOS HO2S

Hose Clamp

Simple ring type clamp to seal a hose onto a pipe.
Entry link: Hose Clamp

Hot Idle Compensator

A device to change idle or mixture settings when an engine is hot.
Entry link: Hot Idle Compensator

Hot Spray

The technique of applying paint at elevated temperatures. The elevated temperature reduces the viscosity so that higher solids materials can be sprayed, and allows application with less solvent.
Entry link: Hot Spray

Hot Stamping

A machine forging process using a series of dies to create the completed shape.
Entry link: Hot Stamping

Hot Wire

A small thin wire that is heated an placed in an air flow. The change in temperature is used to determine the rate of air flow.
Entry link: Hot Wire


Entry link: hp


High Tension
Entry link: HT

HT Cables

High tension leads (high voltage) used to supply the spark.
Entry link: HT Cables

HT Leads

High tension leads (high voltage) used to supply the spark.
Entry link: HT Leads


Centre of a wheel or gear or similar.
Entry link: Hub

Hub Nut

Main nut that secures a wheel hub.
Entry link: Hub Nut


The quality by which colours are distinguished from one another, such as">a red from yellow, blue, green, or purple, and all shades in between.
Entry link: Hue


Uneven running of an engine, usually when the mixture is over rich.
Entry link: Hunting


Heating, ventilation and air conditioning.
Entry link: HVAC

HVLP (High Volume, Low Pressure)

Describes a paint gun that uses a high volume and low pressure of atomising air to apply material to a surface. This provides high transfer efficiency and lower overspray.
Entry link: HVLP (High Volume, Low Pressure)


A hybrid vehicle is a vehicle that uses two or more power sources to move the vehicle. The term most commonly refers to hybrid electric vehicles (HEVs), which combine an internal combustion engine and one or more electric motors.
Entry link: Hybrid

Hybrid vehicle

Vehicles that use both a traditional engine (combustion) and a rechargeable system (typically operated by a battery) to improve mileage, cause less pollution, and decrease need for fossil fuel.
Entry link: Hybrid vehicle


A system for transmitting and modifying force by the use of a liquid. Consists of a pump, control devices, hydraulic lines and slave cylinders.
Entry link: Hydraulic

Hydraulic Brake

Brake actuated only by hydraulic pressure.
Entry link: Hydraulic Brake

Hydraulic Clutch

A clutch, operated by fluid pressure.
Entry link: Hydraulic Clutch

Hydraulic Hoses

Hoses that carry fluid under high pressure.
Entry link: Hydraulic Hoses

Hydraulic Lifters

Hydraulic cam followers in the valve opening mechanism.
Entry link: Hydraulic Lifters

Hydraulic Pedestal

Self-adjusting support for a finger tappet in the valve opening mechanism.
Entry link: Hydraulic Pedestal

Hydraulic Pressure

Pressure applied by a fluid.
Entry link: Hydraulic Pressure

Hydraulic Tappets

Self-adjusting cam followers in valve opening mechanism.
Entry link: Hydraulic Tappets

Hydraulic Valves

Valves used to control pressure or flow of a hydraulic fluid.
Entry link: Hydraulic Valves


A compound which contains only carbon and hydrogen, which are distillate by-products of petroleum, natural gas and coal.
Entry link: Hydrocarbon

Hydrocarbon (HC)

Chemical compound which contains only, or principally, Carbon and Hydrogen. The principal constituent of liquid fossil fuels.
Entry link: Hydrocarbon (HC)

Hydrocarbon Emissions

Fuel vapours released into the atmosphere from a vehicle exhaust or fuel tank.
Entry link: Hydrocarbon Emissions


To break down (a hydrocarbon) by the process of hydrocracking. This is a catalytic cracking process of breaking down large hydrocarbon molecules into smaller ones
Entry link: Hydrocrack


Reaction with water. Usually refers to a decomposition process leading to paint failure.
Entry link: Hydrolysis


Instrument used for measuring specific gravity/relative density of a liquid (coolant, battery electrolyte).
Entry link: Hydrometer

Hydropneumatic Suspension

A suspension system using a liquid to transfer suspension movements to pneumatic (gas) springs.
Entry link: Hydropneumatic Suspension


Instrument used for measuring relative humidity - in an automotive context it is used to check moisture content of brake fluid.
Entry link: Hygrometer


A paint film or other solid that readily absorbs water.
Entry link: Hygroscopic

Hypoid Gearing

Bevel gear with the axes of the driving and driven shafts at right angles, but not in the same plane, giving some sliding action between teeth. Widely used in rear axle final drives.
Entry link: Hypoid Gearing


A characteristic of materials, sensors and sometimes instruments to make their behaviour dependent on the immediate history to which they have been subjected. Typically the final settling point is different when approached from above to when it is approached from below
Entry link: Hysteresis



Independent Front Suspension. Also inertia fuel shut off switch used to switch off an electrical fuel pump or diesel fuel pump solenoid when the vehicle is involved in an accident."
Entry link: I.F.S


Independent Rear Suspension."
Entry link: I.R.S


Idle adjust. Idle speed adjust.
Entry link: IA ISA


Idle Air Control
Entry link: IAC


Intake air temperature sensor used in electronic fuel injection as a correction factor for the quantity of fuel to be delivered.
Entry link: IAT


Intake Air Temperature Sensor
Entry link: IATS


Integrated Circuit
Entry link: IC


In Car Entertainment system.
Entry link: ICE


Ignition Control Module.
Entry link: ICM


Idle Control Solenoid
Entry link: ICS


Information and Communication Technology.
Entry link: ICT


Inside Diameter
Entry link: ID


Indirect injection of diesel fuel into a pre-combustion or swirl chamber in the cylinder head.
Entry link: IDI


Term used to describe an engine running at a speed when the throttle has not been depressed. Also used to describe a lazy technician...
Entry link: Idle

Idle Air Control (IAC)

Idle air control. An air valve on fuel injection systems to increase the air flow and idle speed of a cold engine and during warm up.
Entry link: Idle Air Control (IAC)

Idle Control Components

Parts that are designed to keep the engine idle speed at a set level.
Entry link: Idle Control Components

Idle Mixture

The fuel strength or air/fuel ratio.
Entry link: Idle Mixture

Idle Speed

Rotational speed of an engine on no-load and minimum throttle setting. Also tick over and curb idle.
Entry link: Idle Speed

Idler Arm

A steering arm parallel to the Pitman arm (drop arm) and connected to it by a centre track rod.
Entry link: Idler Arm

Idler Gear

(1) A gear between two others that does not affect the gear ratio. Any gearwheel between the driving and driven gears in a gear train, the shaft of which serves only to bear and locate the gear, and is therefore 'idle'. The idler gear may serve to reverse the rotation of the driven wheel, so that it rotates in the same direction as the driving wheel. (2) An intermediate or tensioning pulley for a belt drive.
Entry link: Idler Gear


Describes an engine running at idle speed (usually 700 to 800 rev/min).
Entry link: Idling


International electrotechnical commission
Entry link: IEC


Indirect Fuel Injection
Entry link: IFI


The insulated gate bipolar transistor or IGBT is a three-terminal power semiconductor device, noted for high efficiency and fast switching.
Entry link: IGBT


Entry link: IGN


The part of an air bag unit that sets the inflation process in to action.
Entry link: Igniter

Ignition - IGN

Starting of combustion. Setting fire to a flammable substance. In a petrol engine the spark jumping the spark plug electrodes that starts the combustion process.
Entry link: Ignition - IGN

Ignition Advance

The automatic bringing forward of the ignition spark in relation to the engine speed.
Entry link: Ignition Advance

Ignition circuit

The system used to connect components involved in producing a high voltage at the spark plugs.
Entry link: Ignition circuit

Ignition Coil

An electrical transformer that increases the battery voltage to a high tension capable of arcing across the gap of spark plug electrodes.
Entry link: Ignition Coil

Ignition Coil - IGC

An electrical transformer that increases the battery voltage to a high tension capable of arcing across the gap of spark plug electrodes.
Entry link: Ignition Coil - IGC

Ignition Distributor

A component in the ignition system that houses the primary circuit switching device and the secondary circuit distribution components.
Entry link: Ignition Distributor

Ignition Lag

A short delay after injection before the fuel ignites.
Entry link: Ignition Lag

Ignition Module

The electronic unit that switches the ignition coil on and off in response to a signal from a pulse generator.
Entry link: Ignition Module

Ignition Switch

The engine ignition and vehicle electrical circuits control switch used by the driver to start and stop the engine.
Entry link: Ignition Switch

Ignition Timing

The static and dynamic settings of the ignition distributor or in the engine control module (ECM) that control the ignition coil secondary circuit output and spark for starting the combustion process in the engine.
Entry link: Ignition Timing


Lighting up, making bright.
Entry link: Illumination


Integrated Motor Assist is Honda's term for their hybrid propulsion system. This includes the electric motor/generator, 144v battery pack, controlling electronics and the wiring that connects them all together. ISG or ISA is used by some manufacturers, Integrated Starter Generator or Alternator.
Entry link: IMA


Taking place without delay.

Entry link: Immediately

Immiscible (non-miscible)

Incapable of mixing in or blending with other components.
Entry link: Immiscible (non-miscible)


Usually part of an alarm system. It cuts off the ignition or fuel to prevent a vehicle from being started and stolen.
Entry link: Immobiliser

Impact Switch

A switch that operates when the car impacts something. Used as a safety device to cut off a fuel pump.
Entry link: Impact Switch

Impact Tools

Power tools that use a high frequency hammering action for the removal and installation of nuts and bolts, for drilling and chiselling. Impact tools should only be used with sockets, drills and chisels made for that purpose. The use of normal hand tools form impact is hazardous as these may shatter in use.
Entry link: Impact Tools


Vaned disc that creates flow by centrifugal force (water pump). In a torque converter it is driven from the engine to force liquid onto the turbine.
Entry link: Impeller


Old British standard of measurement using yards, feet and inches.
Entry link: Imperial

Imperial Measurement

Defined by three measures - the gallon, the yard and the pound.
Entry link: Imperial Measurement

In-line Engine

A engine fitted along the axis of a motor vehicle.
Entry link: In-line Engine

Inboard Brakes

Brake units fitted on the final drive casing and output shafts rather than on the wheel hub and carrier.
Entry link: Inboard Brakes


Light given off by a high temperature object. Usually describes a bulb filament.
Entry link: Incandescence

Included Angle

Camber and steering swivel (king pin) inclinations (angles) added together.
Entry link: Included Angle

Incoming Telephone Call

To receive a telephone call.
Entry link: Incoming Telephone Call

Independent Suspension

Suspension fitted to each wheel."
Entry link: Independent Suspension

Indirect Injection

Diesel engine design where fuel is injected into a pre-combustion chamber fitted inside the cylinder head.
Entry link: Indirect Injection

Induced Voltage

Naturally occurring voltage in a conductor when subjected a magnetic flux.
Entry link: Induced Voltage


Property of a coil such that an increase in current causes an increase in magnetism, which in turn tends to prevent the original increase in current. See also Lens's law.
Entry link: Inductance


1. The drawing in of a gas or fluid. 2. Process of causing an electrical potential in a conductor due to relative movement of a magnetic field.
Entry link: Induction

Induction Period

An allotted amount of time upon mixing of components for compatibilization. The process is common among the use of epoxy/polyamide coatings.
Entry link: Induction Period

Induction Stroke

First stroke of four stroke cycle when air and fuel enter the engine as the piston moves down the cylinder. Also known as the intake stroke.
Entry link: Induction Stroke

Inductive Coil

All coils possess inductance. This is the property that resists changes in current flow.
Entry link: Inductive Coil

Inductive Generator

A magnetic/electrical pulse generator used as a sensor in electronic control systems. It uses an iron core and electrical winding to induce an electrical current when passed by a toothed wheel or rotor. Also known as a magnetic pulse generator.
Entry link: Inductive Generator

Inductive Sensor

A coil and magnet used in conjunction with a trigger wheel. It produces a sine wave output with a frequency proportional to speed.
Entry link: Inductive Sensor

Industrial Fallout

Chemical compounds present in the air which are deposited on the horizontal surfaces of vehicles and which may damage the finish.
Entry link: Industrial Fallout

Inert Gas

A non-reactive gas element.
Entry link: Inert Gas


The force that holds a body stationary or in uniform motion.
Entry link: Inertia

Inertia Reel

Type of seat belt that holds spare webbing on a reel and locks the reel on impact. This is performed by a swinging weighted ball and lever that locks the belt reel ratchet wheel with a pawl.
Entry link: Inertia Reel

Inertia Switch

A switch that operates by the inertia (need to stay at a constant speed or state of rest) of a mass. Usually used to cut off supply to a fuel pump in case of a crash.
Entry link: Inertia Switch


The general increase in the price of goods and services.
Entry link: Inflation


Light energy that produces radiated heat, used for speeding up the curing of paint, filler, etc.
Entry link: Infrared

Infrared Light

That portion of the spectrum responsible for most of the heating effects of the sun's light. Not visible to the human eye.
Entry link: Infrared Light

Infrared Lighting

Infrared light is outside the visible spectrum. When used for lighting, a special detector is also needed.
Entry link: Infrared Lighting

Infrared Sensor

A sensor that is sensitive and produces a signal in response to infrared light.
Entry link: Infrared Sensor


Take in by swallowing or absorbing.
Entry link: Ingestion


Breathing in.
Entry link: Inhalation


To hinder or to restrain progress.
Entry link: Inhibit


A chemical added to retard or prevent a particular reaction.
Entry link: Inhibitor

Inhibitor Switch

A simple switch that prevents the operation of a circuit. A good example is the switch in an automatic transmission gearbox that prevents operation of the starter motor when drive or reverse is engaged.
Entry link: Inhibitor Switch


A chemical that restricts or reduces the chemical reactions. In a cooling system an inhibitor is added to prevent corrosion of the engine from the ethylene glycol content of the antifreeze.
Entry link: Inhibitors

Initial diagnostic assessment

This is carried out to find a candidates strengths and weaknesses, current levels of attainment and potential.
Entry link: Initial diagnostic assessment


A chemical added to help start a chemical reaction such as polymerization or curing.
Entry link: Initiator


Injector valve.
Entry link: INJ


Of fuel by pressure into inlet manifolds (petrol) or combustion chamber (diesel).
Entry link: Injection

Injection Lag

A short time delay between actuation and actual operation of an injector.
Entry link: Injection Lag

Injection Timing

Point within the four-stroke cycle when injection occurs. Similar to ignition timing on petrol engines.
Entry link: Injection Timing


Control valve and nozzle used to inject and atomise fuel.
Entry link: Injector

Injector lag

A short time delay between actuation and actual operation of an injector.
Entry link: Injector lag

Injector Nozzle

The tip of a fuel injector, which is drilled to produce a particular spray pattern.
Entry link: Injector Nozzle

Injector Pulse Width

When viewed on an oscilloscope, the horizontal width of the trace. This represents the open time of the injector.
Entry link: Injector Pulse Width

Injector Pump

Fuel pump that produces the timed high pressure pulses for the injection and timing of fuel delivery on a diesel engine.
Entry link: Injector Pump

Inlet Manifold

Ducting that connects the carburettor/fuel injection components to the inlet ports in the cylinder head.
Entry link: Inlet Manifold

Inlet Ports

The way in to the engine for fuel/air mixture.
Entry link: Inlet Ports

Inlet Valve

Valve in the inlet port that allows air or air/fuel mixture into an engine.
Entry link: Inlet Valve

Inline Pump

Type of diesel fuel injection pump with the pump elements in line.
Entry link: Inline Pump

Inner Races

The inside rings of ball or roller bearings.
Entry link: Inner Races

Inner Tube