Automotive Glossary

Automotive Glossary

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A deposit that builds up in fuel components. It is similar to varnish.


Paints that dry by evaporative loss of solvent, e.g. Cellulose and 1K Acrylics. The film remains soluble in and susceptible to attack by the same or similar solvents.

Ladder Chassis

A chassis construction consisting of two longitudinal side members and a series of cross members. The finished chassis has the appearance of a ladder.


Carrying a load.

Lag (Valve)

The term applied to valves which remain open after the piston has passed tdc or bdc at the end of a stroke in the four stroke cycle.


Greek letter like an upside down y. It represents the ideal air to fuel ratio of 14.7:1.

Lambda 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 EOS Exhaust Oxygen Sensor.


A layered component made from thin sheets of material.

Laminated Glass

Plastic or vinyl core with thin glass each side. An approved glass construction for vehicle windscreens.

Laminated Spring

A leaf spring with multiple leaves.


The sliding areas on pistons either side of ring grooves or fluid passages. The area on shafts that an oil seal lip seals against.

Lap and Diagonal Belt

Type of seat belt that has a single belt threaded across the lap and shoulder and anchored at three points. The anchorage points are both sides of the lap and on the pillar above the shoulder of the wearer. Also known as a three point seat belt.

Lap Belt

Type of seat belt that has a lap restraint belt only.

Large Class 4

A Class 4 vehicle with a DGW greater than 2500kg.

Latching Relay

A relay that latches into a set position when first operated and then back to its rest position next time it is operated.

Latent Heat

The heat energy that is needed to bring about a change of state of a material. During a change of state the temperature remains constant.

Lateral Forces

Sideways forces.

Lateral Runout

Movement from side to side in a rotating component.


Sideways to the length of the vehicle.


An emulsion; usually a dispersion of a polymer in water.

Layrub Joint

A type of limited angle constant velocity joint consisting of an enclosed rubber disc with two pairs of sleeves which are attached to mountings on the ends of the shafts.


The shaft in a manual gearbox carrying the gear cluster and meshing with the constant mesh gears. Also known as a countershaft.

Lazy Lock

Term used to describe the automatic closing of windows when central locking is operated.

lb. ft.

Pound Feet"


Low Compression.


Liquid Crystal Display. An electronic display device using liquid crystals in a glass sandwich. The glass has an inner transparent series of conductors and polarizing filters. Electrical signals to the conductors rearranges the liquid crystals to form digital or other images.

Lead (Valve)

The term applied to valves which open before the piston has passed tdc or bdc at the beginning of a stroke in the four stroke cycle.

Lead Oxide

Material used for the positive plate material in a battery.

Leading Edge

The front edge of a brake shoe in relation to the direction of rotation of the brake drum.

Leading Shoe

A brake shoe that has a leading edge making first contact when applied. Also primary shoe.

Leaf Spring

Metal spring used on vehicle suspensions. Consists of one or more steel strips clamped together with a mounting eye at each end. The front eye is used for fixing to the chassis and the rear eye for fixing to a swinging shackle. Or it may have a mounting eye at the front and a flat end plate for a slipper shackle at the rear.

Lean Fuel/Air Mixture

A fuel/air mixture with a ratio less than the stoichiometric ratio of 14.7:1. A mixture strength with an excess of air and therefore oxygen.

Learning style

The way a person takes in, understands, expresses and remembers information; the way a person learns best.


A tough material produced from the skin of animals, by tanning or similar process.


Light emitting diode. An electronic diode that emits light when an electrical current passes through it.

Legal Rights

Statutory rights within law.



Let-down Panel

Panel made by a paint technician with different methods of application and amounts of material, resulting in different shades of the same colour.


The flowing out of a paint film, occurring from the time the paint particles form a wet film on the surface to the time the film hardens and dries.


A rigid rod or bar that moves about a fixed point.


The use of levers to gain a mechanical advantage.


Left-Hand Drive


Untrue and harmful information.


Collection of materials i.e. books or cd's.

Lift Pump

A low pressure pump used to supply a carburettor or diesel injector pump with fuel. Driven mechanically from a cam in the engine or electrically from the battery.


Attack by the solvent in a newly-applied paint on the substrate which results in distortion or wrinkling of the preceding dried or partially cured layers.

Light Meter

A meter that measures light intensity.


The brightness of a paint or object compared to a perfect white. Measured by the amount of light reflected by a surface. A perfect white is one which reflects 100% of the light in the visible spectrum.

Limit Switch

A switch that operates by a linkage at the limit of its movement. For example, a wiper motor has a switch that operates when the blades are in the park position.

Limited Slip Differential

Final drive differential with a clutch or other device to limit the differential action when one wheel loses traction.

Limp Home

Electronic control systems on later vehicles can substitute faulty sensor signals and therefore a vehicle can 'limp home' even when a fault occurs.


The LIN-Bus (Local Interconnect Network) is a vehicle bus standard or computer networking bus-system used within current automotive network architectures. Local interconnect network (LIN) is a single-master, multiple-slave networking architecture originally developed for automotive sensor and actuator networking applications.


For an equal increase in one variable an equal increase occurs in another.

Linear Valve

A valve where the movement is proportional to the change in opening size.

Liner (Cylinder)

A steel sleeve used to form a running surface for pistons in an engine. Also known as a cylinder sleeve.


The friction material attached to brake pads, shoes and clutch friction plates.


General term used to describe a collection of components that operate something.

Lip Seal

An oil seal with a lip that is reinforced with a coil spring and is used to retain oil on a revolving or reciprocating shaft.

Liquid Lever

Hydraulic cylinders that increase the force applied.

Little End

End of the con rod that fits to the piston.

Live Axle

An axle that transmits a drive to the wheels. Also known as a drive axle.

Live Feed

Electrical supply from (usually) the battery positive, possibly via the ignition switch and a fuse.


Description of how hard an engine is working.

Load Carrying Member

A component of a chassis which carries or supports the weight of the vehicle, the engine or other mechanical system. Any other component that carries a load.

Load Sensing Valve

A valve in the rear brake circuit of a goods carrying vehicle that responds to the weight of load to vary the braking effort of the rear wheels.

Loading (Clogging)

The build-up of flatting residue between the abrasive particles on flatting papers or discs during use. Loading reduces the cutting effectiveness of the abrasive.


The lever component of a cam set on an eccentric orbit from the centre axis of the shaft.

Lock (Steering)

The amount that the front wheels are able to turn from the straight ahead position to fully turned. Measures either as an angle of turn or the diameter of the minimum turning circle.

Lock Nut

A nut that is used to lock another nut or threaded component in position on a threaded rod or stud. Also jam nut - US term.

Lock Tab

Special washer that can be bent over to lock a nut or similar.

Lock-up Clutch

Automatically operated clutch in a torque converter applied during constant speeds to lock the input and output components together.

Logic Gate

A simple electronic device, which has an output that is dependent on its input of combinations of inputs. Common types are described as AND, OR and NOT.

Logic Probe

High resistance tester (so it does not load the circuit), that is used to check the logic state (1/0 or high/low voltage) of a circuit.


Long life, long duration of service,durability


Any axis running from the front to the rear of a vehicle or other object.

Longitudinal Axis

Any axis running from the front to the rear of a vehicle and parallel with the ground and the sides of the vehicle. The main vehicle axis runs through the centre of gravity of the vehicle.

Longitudinal Forces

Forces acting along the length of a vehicle.


The collection of vehicle cables wound together with an insulation tape. Also known as a 'wiring harness'.


Limited Operation Strategy. Get home or limp home mode of ECM when system failures occur.

Low Boilers

Solvents with low boiling points, usually less than 50 degrees Celsius.

Low Film Build

The condition of a paint film when it is too thin to provide protection to the substrate or withstand environmental conditions.

Low Profile Tyre

Tyre with an aspect ratio less than 80%. The depth of the tyre is less than the width by the percentage value.

Low Tension

The term used for the low voltage in the primary circuit of the ignition system.

Low Tension Circuit

The ignition coil primary or control circuit operating at battery voltage (low tension).

Lower Control Arm

The lower and longer wishbone in an independent suspension system.

Lower Quartile

Data is split into 4 equal quarters. The lowest quarter is referred to as the Lower Quartile. For example the Lower Quartile of 100 is the lowest 25 of the numbers.


Liquid Petroleum Gas.


Long Term Fuel Trim


Oil, for example, to prevent surface contact.


Minimise friction with oil, grease, etc.


Lock-up solenoid. Operates with PCM signal to apply the torque converter lock-up clutch.


Gloss or sheen of a finish.


Long Wheel-Base

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