Automotive Glossary

Automotive Glossary

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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."


Independent Rear Suspension."


Idle adjust. Idle speed adjust.


Idle Air Control


Intake air temperature sensor used in electronic fuel injection as a correction factor for the quantity of fuel to be delivered.


Intake Air Temperature Sensor


Integrated Circuit


In Car Entertainment system.


Ignition Control Module.


Idle Control Solenoid


Information and Communication Technology.


Inside Diameter


Indirect injection of diesel fuel into a pre-combustion or swirl chamber in the cylinder head.


Term used to describe an engine running at a speed when the throttle has not been depressed. Also used to describe a lazy technician...

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.

Idle Control Components

Parts that are designed to keep the engine idle speed at a set level.

Idle Mixture

The fuel strength or air/fuel ratio.

Idle Speed

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

Idler Arm

A steering arm parallel to the Pitman arm (drop arm) and connected to it by a centre track rod.

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.


Describes an engine running at idle speed (usually 700 to 800 rev/min).


International electrotechnical commission


Indirect Fuel Injection


The insulated gate bipolar transistor or IGBT is a three-terminal power semiconductor device, noted for high efficiency and fast switching.




The part of an air bag unit that sets the inflation process in to action.

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.

Ignition Advance

The automatic bringing forward of the ignition spark in relation to the engine speed.

Ignition circuit

The system used to connect components involved in producing a high voltage at the spark plugs.

Ignition Coil

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

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.

Ignition Distributor

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

Ignition Lag

A short delay after injection before the fuel ignites.

Ignition Module

The electronic unit that switches the ignition coil on and off in response to a signal from a pulse generator.

Ignition Switch

The engine ignition and vehicle electrical circuits control switch used by the driver to start and stop the engine.

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.


Lighting up, making bright.


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.


Taking place without delay.

Immiscible (non-miscible)

Incapable of mixing in or blending with other components.


Usually part of an alarm system. It cuts off the ignition or fuel to prevent a vehicle from being started and stolen.

Impact Switch

A switch that operates when the car impacts something. Used as a safety device to cut off a fuel pump.

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.


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.


Old British standard of measurement using yards, feet and inches.

Imperial Measurement

Defined by three measures - the gallon, the yard and the pound.

In-line Engine

A engine fitted along the axis of a motor vehicle.

Inboard Brakes

Brake units fitted on the final drive casing and output shafts rather than on the wheel hub and carrier.


Light given off by a high temperature object. Usually describes a bulb filament.

Included Angle

Camber and steering swivel (king pin) inclinations (angles) added together.

Incoming Telephone Call

To receive a telephone call.

Independent Suspension

Suspension fitted to each wheel."

Indirect Injection

Diesel engine design where fuel is injected into a pre-combustion chamber fitted inside the cylinder head.

Induced Voltage

Naturally occurring voltage in a conductor when subjected a magnetic flux.


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.


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.

Induction Period

An allotted amount of time upon mixing of components for compatibilization. The process is common among the use of epoxy/polyamide coatings.

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.

Inductive Coil

All coils possess inductance. This is the property that resists changes in current flow.

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.

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.

Industrial Fallout

Chemical compounds present in the air which are deposited on the horizontal surfaces of vehicles and which may damage the finish.

Inert Gas

A non-reactive gas element.


The force that holds a body stationary or in uniform motion.

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.

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.


The general increase in the price of goods and services.


Light energy that produces radiated heat, used for speeding up the curing of paint, filler, etc.

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.

Infrared Lighting

Infrared light is outside the visible spectrum. When used for lighting, a special detector is also needed.

Infrared Sensor

A sensor that is sensitive and produces a signal in response to infrared light.


Take in by swallowing or absorbing.


Breathing in.


To hinder or to restrain progress.


A chemical added to retard or prevent a particular reaction.

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.


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.

Initial diagnostic assessment

This is carried out to find a candidates strengths and weaknesses, current levels of attainment and potential.


A chemical added to help start a chemical reaction such as polymerization or curing.


Injector valve.


Of fuel by pressure into inlet manifolds (petrol) or combustion chamber (diesel).

Injection Lag

A short time delay between actuation and actual operation of an injector.

Injection Timing

Point within the four-stroke cycle when injection occurs. Similar to ignition timing on petrol engines.


Control valve and nozzle used to inject and atomise fuel.

Injector lag

A short time delay between actuation and actual operation of an injector.

Injector Nozzle

The tip of a fuel injector, which is drilled to produce a particular spray pattern.

Injector Pulse Width

When viewed on an oscilloscope, the horizontal width of the trace. This represents the open time of the injector.

Injector Pump

Fuel pump that produces the timed high pressure pulses for the injection and timing of fuel delivery on a diesel engine.

Inlet Manifold

Ducting that connects the carburettor/fuel injection components to the inlet ports in the cylinder head.

Inlet Ports

The way in to the engine for fuel/air mixture.

Inlet Valve

Valve in the inlet port that allows air or air/fuel mixture into an engine.

Inline Pump

Type of diesel fuel injection pump with the pump elements in line.

Inner Races

The inside rings of ball or roller bearings.

Inner Tube

The separate sealed air tube on a tyre that is required with certain types of tyre and wheel rim.

Inner Wing

Metal panel structure under the bonnet forming part of the wing.


Power or data that goes into a mechanical unit or electronic control module.

Input Device

A device that allows you to put information into the computer. Egg, keyboard, mouse.

Input Shaft

Shaft that takes drive from the engine into the gearbox.

Insert (Valve Seat)

A steel insert fitted in aluminium and some iron cylinder heads to form a durable seating for the inlet and exhaust valves.


A feature of air brakes designed to give an initial quick application to make up for the time it takes for air pressure change.

Instrument Lights

Illumination for instruments such as the speedometer.

Instrument Panel

The panel in a vehicle fascia that holds the instruments and warning lights. Also dash panel and dashboard.

Insulated Circuit

A vehicle wiring system that does not use the body and chassis as a ground to form a return electrical circuit to the battery and alternator. A separate insulated set of cables connects all components to complete the circuits. Used in vehicles where there is a high fire risk. (Fuel tankers).

Insulation resistance

The resistance to current flow of the insulating materials between circuits and contacts.


Restricts the flow of electricity or heat through the material.

Intake Manifold

See inlet manifold.

Intake Stroke

Alternative term for the induction stroke. First stroke of four stroke cycle when air and fuel enter the engine as the piston moves down the cylinder.

Integral Body Construction

Modern light vehicle body and chassis construction method which has no separate chassis. The strength is built in by the use of stressed and reinforced panels.


To incorporate something into something else or to unite into a whole.

Integrated Circuit (IC)

An electronic device consisting of transistors, diodes and other components in a single unit and usually having a specific function.


Data corruption refers to errors in computer data that occur during transmission, retrieval, or processing, introducing unintended changes to the original data. Computer storage and transmission systems use a number of measures to provide data integrity, or in other words the lack of errors.

Intelligent device

A component that has some ability to monitor itself and react to changes.


A device which converts low pressure fluid power into higher pressure fluid power (used by some injection systems)

Inter-Quartile Mean

The average of the values in the inter-quartile range.

Inter-Quartile Range

The range of numbers with the upper and lower quartiles removed.


Two-way communication.


An air to air radiator type heat exchanger fitted after a turbocharger in the air intake ducting to cool the intake air before it enters the engine.

Interference 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 less than the outer dimension of the inner component.

Interior Lights

Lights inside a vehicle for illumination purposes.

Interleaf Friction

Friction between spring leaves that produces a damping effect.


Part of a manual gearbox selector mechanism that prevents the engagement of two gears at the same time.

Intermediate Gear

Any gear in a transmission gearbox other than top and bottom or reverse.

Intermediate Shaft

A shaft between the input and output shafts, usually as part of a gearbox.

Internal Combustion

Engine where fuel is burnt inside cylinders.

Internal Customer

One inside of an organisation.

Internal Damping

A feature of some suspension components where friction tends to reduce oscillations.

Internal Resistance

Describes the resistance of a component that is the combination of all its internal parts. Even a battery has some resistance inside it.

Internal Splines

Splines (teeth) inside a shaft or tube.

Internal Taper

A hole that narrows.

Internal verification

The process whereby a centre ensures it operates consistently and to national standards in interpreting and assessing the key skills.

Internal Windings

Windings inside a component.


A worldwide network of computers that allows us to view the World Wide Web.


To understand and be able to explain something.


To make somebody feel uncomfortable, timid or even fearful.


An atom with positive or negative charge due to gain or loss of an electron.


Integrated Power Unit.


All colours that contain aluminium, mica, or other particles that impart a metallic appearance to the colour.

Irradiation Treatment

A process where something is acted upon by radiation from a radioactive substance - it is used to make some foodstuffs last longer - but is a contentious issue!


Inertia Switch.


Idle Speed Control. This term is usually used when a stepper motor or solenoid is used for idle speed increases during engine warm-up and when ancillary systems are in use.


International Standards Organization


A fuel used in research tests as a comparison when determining the octane rating of fuels. Octane value of 100.


A chemical found in the hardening agent used with acrylic urethane and other two component reaction type paints. The introduction of Isocyanates in hardeners led to the requirement for air-fed respirators in the vehicle painting industry


Information Technology


Ignition Timing Control System


Idle Tracking Switch

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