Friday, 23 April 2021, 11:20 AM
Site: IMI eLearning
Course: IMI eLearning (IMI eLearning)
Glossary: Automotive Glossary


Anti-lock braking system.


American Petroleum Institute.

A.P.I. (C)

American Petroleum Institute classification for oils suitable for diesel (compression ignition engines).

A.P.I. (S)

American Petroleum Institute classification for oils suitable for gasoline (spark ignition) engines.


Engine lubricating oil classification suitable for basic petrol and diesel engines.


Engine lubricating oil classification suitable for modern engines.


Air Conditioning

A/C - Air Conditioning

Air conditioning system that uses a refrigerant to remove heat from the air entering the passenger compartment.

A/D Converter

An electronic device used to convert analog values to digital signals for electronic control units and instruments.


Air/Fuel Ratio


Automatic transmission.


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.


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.


Wearing away of a surface by some external force, such as sanding.


Substance used to wear away or smooth a surface by friction.


Substances used to wear away a surface by friction.


Antilock braking system.

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.


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


Of heat: Takes in heat energy. Of sound: Takes in sound energy.


Air Bypass Solenoid Valve


Alternating Current

AC - Alternating Current

An electrical current that flows in forward and reverse bias alternately.


To speed up a process.


Increasing velocity or speed.


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

Accelerator Pump

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


A hydraulic device that dampens the pulses and retains a residual pressure in a hydraulic circuit.


How close the data given is to the true value.


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.


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


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.

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.

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.

Ackerman Principle

System of steering that produces wheel turning axes around a common point.


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

Acrylic Urethane

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


Air conditioning switch.

ACT - Air Charge Temperature

Air charge temperature sensor measures the intake air temperature on fuel injection systems.


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


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


Air Charge Temperature Sensor


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


General term used to describe a device that allows one component to fit with another.

Adaptive Memory

A computer memory process that allows for changes in an open-loop mode.


A chemical added to improve the properties or performance of something.


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.


The phenomenon by which one material is attached to another by means of surface attraction.


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


Guidance offered by someone.


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).


Air mixture in a hydraulic liquid that reduces the performance of a hydraulic system.

Aesthetic Value

A value put on how nice or appealing something looks.


Air Flow Control


Air Flow Meter


Air Flow Sensor


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.


A paint stirrer.

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.

Air Bleed Valve

An automatic device used on fuel injection systems to provide fast idle during cold start and warm up.

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.

Air Charge

Description of the amount of air taken into an engine on the induction stroke.

Air Cleaners/Filters

Canisters holding paper, plastic foam or gauze elements to trap dirt and grit.

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.

Air Flow

Movement of a quantity of air past a point in a set time.

Air Flow Meter

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

Air Flow Sensor Plate

A plate used to sense the movement of air and therefore control fuel quantity.

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.

Air Horn

The air inlet side of a carburettor or throttle body assembly.

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.

Air Intake Duct

A pipe or similar used as part of the intake manifold or general system.

Air Line

A pipe that delivers compressed air.

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.

Air Ratchet

A ratchet wrench driven by compressed air.

Air Resistance

Friction force caused by, for example, a vehicle moving through the air.

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.

Air Temperature Sensor

Electronic device that provides information for engine management systems and frost warning indicator.

Air-fuel Ratio

The air and fuel mixture strength ratio.

Airflow Meter

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

Airflow Sensor Plate

Mechanical fuel injection component that moves in proportion to the air intake and sets fuelling accordingly.

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.


A pipe that delivers compressed air.


Assembly Line Communications Link


Assembly line communication or diagnostic link. A multisocket connector for attaching a diagnostic tool to a vehicle electronic system.

Alcoholics Anonymous

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


Assembly Line Data Link


Bringing into line.


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


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


A name used to describe a hexagonal key.


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

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.


An electrical generator attached to and driven by a motor vehicle engine.

Alternator Brushes

Soft carbon brushes that conduct electricity to the field windings via the slip rings.


Non-ferrous metal used as a substrate or a pigment.

Aluminium Oxide

Sharp and hard abrasive - used in dry-flatting Production papers

Ambient Pressure

Air pressure in the surrounding area.

Ambient Temperature

Temperature of the air surrounding an object.


Instrument for measuring electrical current.


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.


Strength of an electrical current in amperes.

Ampere (Amp)

Electrical unit for measuring the flow of electricity in a circuit.


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.


An increased electrical voltage and/or current compared to say the original signal.


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


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.


Short for Ampere (unit of electrical current)


Used to describe a sealant that dries when air or oxygen is excluded.


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

Analog Gauge

An instrument readout that displays using a moving needle or similar method.


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

Analogue Gauge

An instrument readout that displays using a moving needle or similar method.

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'

Annual Income

Amount of money you earn each year.


The outer gear with internal teeth on an epicyclic gear train.


A positive connection.

Anodised Aluminium

A surface treatment for aluminium that adds an oxidised coating to harden the surface of the component.


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


Protective coating applied on metal surfaces to prevent corrosion.


A chemical such as ethylene glycol, added to the cooling water of an engine to lower the freezing point for winter operation.


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.

Anti-roll Bars

Suspension component that reduces vehicle roll.

Anti-skinning Agents

Chemicals added to a paint to help prevent the formation of a surface film during storage.

Anti-trap Function

Facility to prevent electric windows closing and trapping something - your fingers for example! See also Bounce Back.


Additive put in the cooling system to prevent freezing.


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

Antivirus Software

A software package that prevents computer viruses from damaging or destroying the system.


Another name for a computer program such as Microsoft Word.

Applied Solids

Solids that remain on the substrate being coated or painted.


Absolute Pressure Sensor

APS - Absolute Pressure Sensor

A barometric pressure sensor used to compare atmospheric and manifold pressures in electric fuel injection systems.


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


Describes a water-based solution or suspension (see 'waterborne').


Conduction of electricity across a gap. An arc is caused as contacts open.


Length x width


Electrical windings around the core fixed to the spindle of a motor or dynamo.


The smell of something such as perfume or worse...


A type of solvent based on benzene ring molecules.


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


Airbag System Diagnostic Module

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.


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


The teacher or tutor, who assesses the portfolio of evidence.


A description of objects that are different on each side of their centre line.


After Top Dead Centre

ATDC - After Top Dead Center

ATDC - Before Top Dead Centre.

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.


Automatic Transmission Fluid.


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


The air that surrounds the Earth's surface.

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.


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


Relating to the atom...

Atomic clock

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


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.


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


Breaking up of fuel into fine particles during induction into an engine.


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


Air Temperature Sensor


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


See Automatic Transmission

Automatic Adjusters

Brake components that automatically take up wear to keep brake shoes or pads close to the drum or rotor.

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.

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.

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.

Auxiliary Air Valve

A valve used to control auxiliary air flow.

Auxiliary Components

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

Auxiliary Lights

Extra, non-essential lights such as front spotlights or driving lights.

Auxiliary shafts

Shafts that are used on some engines for balance or to drive other components.

Avalanche Diode

A diode that conducts when a value voltage is applied. Used to protect circuits from overload.


The sum divided by the number of items.

Awarding body

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


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.

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.

Axial Loading

Along the axis of a shaft.

Axial Motion

Movement along or parallel to the axis of a shaft.


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


Horizontal transverse shaft or beam with spindles on which road wheels are mounted.

Axle Loading

Term used to describe the forces acting on an axle.

Axle Mounting

Method of fixing the axle to the body or springs.

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.

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.