Automotive Glossary

Automotive Glossary

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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.


Cold filter plugging point. Applies to diesel fuel with a cold weather additive."


Computer Controlled Coil Ignition

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.


A metal used in the manufacture of durable but expensive red and yellow pigments.


A soft grey metallic element used a component in driers and pigments.

Calcium Carbonate

An extender pigment, also known as "whiting."


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.


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.

Calibrated Aperture

An accurate size hole to control flow.

Calibrated Float

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

Calibration Resistor

A variable resistance that is used to set the basic position of a circuit.


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.

Caliper Piston

A slave cylinder in a brake caliper.


Calibration Pack


(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.

Cam Belt

Belt, usually made of reinforced rubber, which drives the cam from the crank.

Cam Linkage

A cam shaped (egg shaped) part.

Cam Lobe

High point of a cam which operates components.

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.

Cam Ring

A shaped ring with a cam shape.


(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.


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.


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


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

CAN message

The information transmitted on a data bus from one node to another.


Canister Purge Solenoid Valve

Cap (Tire Valve)

Air Valve. Secondary air valve for an inflated tire.


An ability to store an electrical charge in two conductors separated by an insulator.


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

Capacity (engine)

Applied to the sum total of the swept volumes for all cylinders in an engine. Also known as 'total displacement'.

Carbon Black

A black pigment manufactured by collecting the carbon resulting from incomplete combustion of natural gas.

Carbon Monoxide (CO)

Polluting, odourless, toxic (poisonous) gas produced by incomplete combustion of fuel.


See Carburettor.


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

Cardan Joint

A drive shaft universal joint consisting of two yokes and a cross bearing. Also Hooke's joint.


Crank Angle Sensor


A metal forming process where molten metal is poured or injected into a mould.


(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.

Castor Angle

Angle in side elevation between the steering and vertical axis.


A substance that causes a chemical reaction when it is mixed with another substance.

Catalytic Converter

Uses platinum, palladium and rhodium to change pollutants in exhaust gases to harmless substances.

Catch Up

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


A negative connection.

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.


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


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.


Cubic Centimetres


Cold cranking amps (a rating for batteries)


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).


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.


Capacitor Discharge Ignition

CDI (Ignition)

Capacitor discharge ignition system that uses a capacitor to produce the high tension for arcing across the electrodes of the spark plug.


Cold Engine Air Bleed


Central Electronic Control Unit


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.

Cell Caps

Removable covers for a battery cell.

Center Bearings

See Centre Bearings.

Center of Gravity

See Centre of Gravity.

Centre Bearings

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

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.

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.

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.

Centrifugal Force

The outward movement felt as a car turns a sharp corner.

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.


Cold Enrichment Rod


Cold Engine Sensor Switch

Cetane Number

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

Cetane Rating

See cetane number.


Central Fuel Injection

CFI (Fuel Injection)

Usually centre point fuel injection system but sometimes used for continuous fuel injection.


Cubic Feet Per Minute


Used to describe the unintentional action of one component rubbing against another.


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


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

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.

Charge Current

See charge rate.


Process of building up the level of charge in a battery or capacitor.

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.


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.

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.


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.


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.

Chemical Bond

A reaction between atoms that causes a force such as to create a bond.

Chemical Cartridge Respirator

A respirator which uses a cartridge containing various chemical substances to purify inhaled air of certain gases and vapours.

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.

Chemical Treatment

A process that uses chemical to bring about a change in something.


Description of an integrated circuit where the circuit is built on a silicon chip.


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


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.

Choke Flap

The butterfly type valve that restricts the flow of air.

Chopper Module

An electronic circuit or unit that switches a supply on and off rapidly.


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.


A chemical compound used as a component in primers to provide corrosion protection to metal.

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.


cylinder identification sensor


A complete conducting path.

Circuit Board

A board used to construct an electronic circuit.

Circuit Breaker

A switch to turn off the current flow in a circuit. Can be manually or automatically operated.

Circuit diagram

A diagram using symbols for electrical and electronic components that represents a real circuit.


The boundary line of a circle.


Continuous Injection System


Crankshaft Position Sensor

CKP Sensor

Abbreviation for the crankshaft position sensor.

Clamp Plate

A simple plate to hold another item securely.


To make clear.


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.


Material used to remove dirt and other impurities from a substrate prior to painting.

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.


A gap between two components.

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.

Clearance Size

A drilling size slightly larger than the nominal size of a thread.

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.


A temporary area used to store copied information.

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


Condition where abrasive paper becomes clogged by the abraded surface coating.

Closed Circuit

Applied to an electrical circuit when the switch is 'on' or the circuit is continuous.

Closed Loop

A system where a change in the output causes a changed input which in turn changes the output and so on...

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.


The formation or presence of a haze in a liquid such as a paint film.


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.

Clutch (Transmission)

Disengages / Engages drive from the engine.

Clutch Fork

See Release Fork.

Clutch Linkage

Mechanism to connect the pedal to the clutch release bearing. May be cable, electrically or hydraulically operated.

Clutch Pack

A set of friction plates and pressure plates in a multi-plate clutch.

Clutch Plate

The friction plate used as part of a clutch.


Camshaft Position Sensor

CMP Sensor

Abbreviation for the camshaft position sensor.


Carbon Monoxide


Carbon Dioxide


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.


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.


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


Driving on very light throttle at a constant speed.


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.


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.

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.

Coil (Ignition)

An electrical transformer that increases the battery voltage to a high tension capable of arcing across the gap of spark plug electrodes.

Coil Spring

A spring that consists of a single length of bar wound into a helix (coil).

Cold Cranking Rating

Applies to a battery's ability to provide a minimum current for a minimum time for starting a cold engine.

Cold Start Enrichment

An increase in the amount of petrol mixed with the air under cold starting conditions.

Cold Start Valve

An extra valve used only when starting from cold.

Cold Starting

Cranking the engine so that it will start and run under cold conditions.


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

Cold-start Valve

An extra valve used only when starting from cold.


Terminal of a transistor that becomes conductive to the emitter when the base is energised.


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


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.

Colour Coat

The single-stage or basecoat that provides the visible colour of a coating system.

Colour Match

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

Colour Retention

The ability of a paint to maintain colour under exposure to light, heat, moisture or other conditions of use.

Colour Sanding

The sanding of a cured or dried paint film to prepare it for polishing or recoating.


The burning of fuel in air.

Combustion Chamber

Area above the piston when it is at TDC where the combustion takes place.

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.

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.


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


Rotating contacts for electrical windings on a generator or motor armature.


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


Provides equal force to mechanically braked wheels.

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.

Composite Materials

Material made up of constituents that remain recognisable.


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).

Compound Gear Train

Two or more pairs of gears.


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


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

Compression Ignition (CI)

Fuel ignited by heated air (diesel).

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).

Compression Ring

A piston ring that helps to contain combustion pressure.

Compression Spring

A spring that is designed to provide force when compressed.

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.


Electrically or mechanically driven pump used to increase pressure of a gas or liquid.

Compressor Wheel

Part of a turbocharger that pumps extra air into the intake and therefore the engine.


Must be completed.

Computer Application

Programs such as Word, Excel and PowerPoint.

Computer Crash

An event that causes the computer to become inactive. This can often result in the loss of unsaved work.

Con Rod

Short for connecting rod, this joins the pistons to the crankshaft.


A term that describes objects that revolve or are fitted around a common centre.


Expressing a lot but in few words.


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.

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.

Condenser (Ignition)

An electrical capacitor that is used in a contact breaker ignition system.


Transfer of electrical or heat energy along material.


A material that allows free movement of electricity or heat through it.

Conductor Foil

General term to describe a type of 'flat' wiring harness.

Cone Clutch

A simple clutch shaped like a cone. Used as part of a synchromesh mechanism.

Cone Pulley

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

Confidential Information

Information that is private and should be protected.

Connecting Rod

The engine component that joins the piston to the crankshaft.

Constant Velocity Joint

A drive shaft joint that transmits drive through an angle without changes in speed.

Construction and Use

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

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.


The rate at which a vehicle uses fuel.

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.


Something which contaminates; an impurity; foreign matter


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


The condition of an electrical circuit when a current will flow.

Continuous Injection

Injectors that inject or 'squirt' all the time.

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.


(see Mapping)


Agreement between parties enforceable in law.


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

Control Flap

A flap that is used to control something! Air temperature for example.

Control Plunger

Part of fuel injection system. Regulates fuel delivery against air flow.

Control Pump

A pump that provides a set pressure.


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

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

Conversion Factor

Used to make it easier when converting from one form of ‘measurement' to another.


To change one expression to another. For example, expressing miles in kilometres.


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.


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


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


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

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.


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).


An acid or other chemical that will chemically react or attack another material.


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

Cost of production

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

Cotter Pin

Tapered pin used to hold shafts into housings. May also be used to describe a split pin.

Counter Gear

See countershaft assembly.

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.


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.


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


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.

Coupling Point

The point or speed at which a torque converter takes up drive.

Courtesy Lights

Lights for the vehicle occupants to use.


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.


General term used to describe a cover.


See single point injection.


Crankshaft position and speed sensor.


Central processing unit. This relates to the main component in an ECU or computer.


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.


A term used to describe turning the engine by the starter motor.


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.

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.


Description of making the engine rotate on the starter motor.


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


Major rotary component of engine that converts piston movement into rotary movement.

Crankshaft Damper

Usually part of the front pulley. A rubber mounted mass reduced torsional vibration.

Crankshaft Oil Seal

Usually radial lip type seals at the front and rear of the crankshaft.

Crankshaft Pulley

Main drive pulley on the end of the crankshaft.

Crankshaft Shell

See Shell Bearings.

Crankshaft Web

Counterbalance weights that are opposite the big end bearing journals.

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.


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.


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.


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

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.


Act of squeezing a connection such as a terminal onto a wire.

Crimped Joint

Termination of cables by squashing tabs on the terminal around the cable.


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

Crocodile Clip

Hand operated clip that, like a crocodile, bites under spring pressure to make a contact. Also alligator clip.

Cross Member

A chassis or support member that runs across a vehicle frame or chassis.

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.

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

Cross-pin (Hooke's) Joint

Type of universal joint with a cross pin and two yokes.


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.


The area exposed if a cut were to be made through the centre of an object.


General term used to describe shafts which are fitted across units rather than along or axially.

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.

Cruise Control

A system that keeps the vehicle at a set speed.


Driving at a constant speed under light throttle conditions.

Crumple Zone

Safety feature of vehicle body, absorbs impacts.


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

Crystalline Structure

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


Cold Start Spark Advance


Cold Start Spark Hold


Closed throttle.


Coolant Temperature Sensor

CTS Sensor

Abbreviation for the engine coolant temperature sensor or switch.


Choke Thermal Vacuum Switch

CTX Transmission

Constantly Variable TransaXle.

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.

Curb Idle

Rotational speed of an engine on no-load and minimum throttle setting. Also tick over and idle.


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

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.


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

Current Regulator

An electrical or electronic device used in generator circuits to control the output current.

Current Relay

A device that usually incorporates a reed switch. It is activated by current flow through a series winding.

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.


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.


Process where fuel supply can be stopped, for example when a vehicle is coasting down.


See Cut-off.

CV (Constant Velocity) Joint

A drive shaft joint that transmits drive through an angle without changes in speed.

CV Joint

A drive shaft joint that transmits drive through an angle without changes in speed.


Control Vacuum Regulator

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.

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.

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.

Cylinder Balance

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

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.

Cylinder Bore

The diameter of the cylinder.

Cylinder Charging

Process of filling a cylinder during the induction stroke.

Cylinder Head

Encloses the top of the cylinder block.


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

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