Automotive Glossary

Automotive Glossary

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Ministry of Transport. Colloquial for the annual inspection test for vehicles.


Mass Air Flow Meter.


Any material with the naturally occurring phenomenon that has the ability to attract iron.

Magnetic field

Magnetic fields surround magnetic materials and electric currents and are detected by the force they exert on other magnetic materials and moving electric charges. The magnetic field at any given point is specified by both a direction and a magnitude (or strength).

Magnetic Flux

The force contained in a magnetic field.

Magnetic Pole

The ends of a magnet where the lines of force originate. The north and south poles.

Magnetic Pulse Generator

A sensor that uses an iron core and electrical winding to induce an electrical current when passed by a toothed wheel or rotor. Also known as an inductive generator.

Magnetic Stand

A holding device for measuring equipment such as a dial test indicator.


A natural force found in iron and some other materials.


The height of a wave. The maximum voltage in an AC wave pattern.

Main Beam

The upper of the two headlamp beams. Also driving beam and upper beam.

Main Bearings

Central journals and bearings on a crankshaft axis mounted in the engine crankcase. The crankshaft rotates in these bearings.

Main Gallery

A tube shaped section cast in to the engine block where other oil feeds are taken from.

Mainline Pressure

The regulated hydraulic pressure in an automatic transmission.

Makeup Air

A system that brings and heats air from the outside to a desired air flow and temperature.


Describes a material that means it can be easily shaped.


Maximum Authorised Mass – The maximum gross weight permissible in GB.


Bars used to locate a component.


Pipes or ducting to route air in or burnt gases out of an engine. Attached to the ports.

Manifold Absolute Pressure

The mean gas absolute static pressure in an engine induction manifold. Absolute pressure is equal to gauge pressure plus atmospheric pressure.

Manifold Vacuum

The depression or low pressure that occurs in the inlet manifold due to the increasing volume above the pistons when they are moving downwards in the cylinders. The airflow into a naturally aspirated engine cannot move quickly enough to fill the additional volume and therefore loses pressure and density.

Manual Transmission

Transmission system where the driver makes the gear shifts by means of a control (gear) lever and linkages to the gearbox.

Manual Valve

The gear selector valve in an automatic transmission operated by the driver.


Manifold Absolute Pressure Sensor. The mean gas absolute static pressure in an engine induction manifold.

Map Light

Small light used in a vehicle for illuminating a map!

MAP Sensor

A pressure sensor used to measure manifold absolute pressure in an engine induction system.


Used to identify opportunities for developing and assessing key skills within the curriculum.

Mapping (Contouring)

Edge of a repaired area under a paint film that shows up after a surface has been repainted.


Application of paper or other material and adhesive tape to cover an object that must be protected from overspray.

Masking Paper

Paper designed to prevent paint from bleeding through.


The total theoretical weight of matter based on its atomic structure. The weight of matter without gravitational pull.

Mass Air Flow Meter

A sensing device in the air intake duct of a fuel injection engine that provides data for control of the quantity of fuel that is injected.

Master Cylinder

The pump on a brake hydraulic system.


Manifold Air Temperature


In painting, to make refinishing colours look the same as the original finish.


A surface with minimal reflection.


A term used to describe any substance as a 'quantity of atoms'.

Matting agent

An additive used to lower the gloss of topcoat, single-stage colours and clearcoats.


Megabyte. Used to measure computer memory. 1 Mb = 1,000,000 bytes or 1024 Kb (kilobytes).


Motor control module

McPherson Strut

Telescopic independently sprung suspension member incorporating a damper, and fixed at its upper end to the body. The lower end is located by linkages which counteract transverse and fore and aft movement. The original system used a track control arm for transverse forces and an anti-roll bar for longitudinal (fore and aft) location. Usually incorporated in a steered front suspension system.


Mixture Control Solenoid


Manifold Charge Temperature


The average value (the sum divided by the number of items).

Mechanical Advantage

The effectiveness of a simple machine, such as a lever, inclined plane, wedge, pulley system or a screw at amplifying a force.

Mechanical Efficiency

The ratio between the actual total output of a machine and the theoretical maximum output.


A combination of a mechanical and electronic control system


The middle number of a series when the data is arranged in ascending order.


Used in 1K OEM finishes, a hard resin used to modify alkyd resins and other films formed used in baking finishes.


The stored data in a microcomputer or electronic control module.

Memory Chip

A chip that stores data.

Memory Keeper

A battery or secondary power source used to preserve ECU memories when the main battery is disconnected. It can often be plugged in to the cigar lighter socket.

Memory Saver

A battery or secondary power source used to preserve ECU memories when the main battery is disconnected. It can often be plugged in to the cigar lighter socket.


Criss-cross fibres to produce a material with very small holes. Used to make filter elements.

Mesh (Gears)

Gear teeth in contact.

Metal Conditioner

An acid-type cleaner which removes small amounts of rust and corrosion left from mechanical metal cleaning. Usually based on Phosphoric Acid solutions.

Metallic Paint

Topcoat which contains metallic pigments, usually in the form of tiny flakes of aluminium. Custom finishes may use other non-ferrous metal flakes such as copper or bronze.


A term used to describe colours that match under a specific light source, but do not match under all light sources. It is primarily caused by the use of pigments that are different to those used in the original formulation.


Measuring the flow rate of a gas or liquid.


When applied to fuel systems a control device for achieving the correct air/fuel mixture strength for specific engine running conditions.

Metering Needle

See metering rod.

Metering Ports

Ports designed to a set size to allow accurate flow of fuel or air.

Metering Rod

A tapered needle in a jet in a carburettor. The taper allows a varied or metered supply dependent on the position of the taper in the jet.


Methyl-alcohol used as a fuel or fuel additive.


The way in which a task is carried out.

Methyl Ethyl Ketone (MEK)

A fast-evaporating solvent.


European standards of measurement based on the metre.

Metric Measurement

A system designed to regulate measurement. Each quantity has a single unit. These include; metre, kilogram, ampere.


Multiport fuel injection. Usually known a port fuel injection or multipoint fuel injection (MPI).


Metal hydride

Micro Processor

A processor on a single integrated circuit or chip. The calculator in a microcomputer or electronic control module.

Micro Switch

A small switch usually operated by a moving mechanism.


A condition which appears as severe dulling of a paint film, but when viewed under magnification, is actually very fine cracking of the painted surface .


Containing lots of very small holes.


Refers to integrated circuit electronics usually involving some form of processor.


Measuring device based on an accurate screw thread. Measurements can be taken to 0.01mm/0.001''.


A measure of paint film thickness, equal to one one-thousandth of a millimetre.


A device that converts sound waves to audio signals.

Microsoft Office

A package of programs including Word Processor (Word), Spreadsheet (Excel), Presentation (PowerPoint), Email and Organisation (Outlook).


1. Essential equipment for use when a technician is hungry...2. High frequency radio waves.

Middle Solvent

A solvent that evaporates at a medium rate, leaving the paint primarily during flash-off.


Malfunction indicator lamp. Dashboard warning light from an electronic control module to signal a system or component failure.


A machining process that uses a rotating blade to cut through the surface of materials.


A motor vehicle constructed or adapted to carry more than eight but no more than sixteen seated passengers (see also Bus).

Ministry Plate

Displays the maximum authorised weights at which a vehicle may be operated. This information supersedes the maximum weights displayed on the Manufacturer’s plate.


The property of materials that mix easily.


Capable of being mixed with or dissolved in other components of a paint, etc.


Uneven running of an engine due to one or more cylinders not working properly.


Represent wrongly with false account (legal).

Mist Coating

A light sprayed coat of a paint material to assist in blending and/or gloss enhancement and metallic control in single-stage colours.

Mixing (Ratio) Stick

Instrument used to gauge the correct ratio of paint material being mixed for ready-to-spray configuration.

Mixing Ratio

The proportion of ingredients to be mixed together to make a ready-to-spray paint.




The most common number in a series.


Modulator-demodulator. Used to convert computer signals so that they can be sent over telephone lines.

Modulating Valve

A valve that can be switched on and off rapidly such as to control its partially open position.

Modulator Assembly

Releases and re-applies fluid pressure to brake units. (ABS). Adjusts and regulates.

Modulator Valve

Flow control valve in power steering pump. In an automatic transmission a valve that responds to manifold vacuum to create hydraulic pressure feedback to the main control assembly.


An electronic control unit for a vehicle system.


Method of Inspection


Relating to atoms formed into molecules.

Molecular Mass

Term used to describe the mass of molecules - usually relating to the mass of the protons and neutrons.


The smallest possible unit or amount of any substance which retains the characteristics of that substance.


Force that keeps a body moving.


The screen that displays information produced on a computer. An output device.


The honeycomb catalyst support element in a catalytic converter.


A petrol fuel injection system using a single point (or monopoint) injector in a throttle body in the inlet air supply and positioned on top of the inlet manifold. Also throttle body injection (TBI).


See also Sunroof... A sunroof that has a clear glass panel, rather than being opaque, so that light can enter the vehicle even when the roof is closed. Some vehicle have a sunroof at the front and a moonroof at the back.


Three wheeled vehicle with max speed of 45km/h, not over 50cc for a petrol engine or 4KW for any other engine or electric motor, not more than 450kg ULW.


Media Oriented Systems Transport. This protocol defines a multimedia fibre-optic point-to-point network implemented in a ring, star or daisy-chain topology over Plastic optical fibres. The MOST bus specifications define the Physical Layer as well as the Application Layer, Network Layer, and Medium Access Control. The MOST bus provides an optical solution for automotive media networks.


Ministry of transport (UK)

Motor Reverse Circuit

An electrical circuit that reverses polarity supplied to a motor.

Motor tricycle

Three wheeled vehicle with wheels symmetrically arranged, a max speed over 45km/h, or engine size over 50cc.


A film defect appearing as blotches or surface imperfections, normally due to metallic or pearlescent pigments not being properly orientated in the paint film.

Mould-Release Agents

Chemical compounds applied to manufacturing moulds which must be removed by a pre-treatment prior to refinishing plastic parts to insure adhesion.


General term for the part of a component, or a separate component, which fits one thing to another.

Mounting Studs

Threaded fixings for an exhaust flange or similar.


Insulated or solid attachments for components/units on the vehicle. Insulated versions absorb vibration and provide some protection from shock loads.


An input device that allows the user to move the pointer around the screen and click on different items to operate computer applications.

Moving Conductor

The armature in a motor or dynamo.


Multi Point Fuel Injection


Miles Per Gallon


Miles Per Hour


Multipoint Fuel Injection.


Multi-Purpose Vehicle




Material Safety Data Sheets.

Muffler (Silencer)

A component in the exhaust system to absorb the gas shock waves and noise in order to reduce the emitted noise from a vehicle engine. Also known as a silencer.

Multi-Plate Brake

A brake that uses several clutch-type plates.

Multi-plate Clutch

A clutch mechanism having a series of friction and steel plates in a clutch drum assembly. One set of plates is splined to the drum and the other to a centre shaft so that drive through the clutch is via the drum, friction faces and the centre shaft.

Multi-vee Belt

A flat drive belt with several ridges or vee shapes running circumferentially (the long way round).

Multigrade Oil

Classification for lubricating oils that change viscosity grades during temperature change. The lower number is the cold temperature grade and the higher number the hot temperature grade. These oils do not thin at the same rate as single grade viscosity oils as the temperature rises. Also known as multiviscosity oils.


An electrical measuring tool with functions for volts, amps and ohms.


A clutch mechanism having a series of friction and steel plates in a clutch drum assembly. One set of plates is splined to the drum and the other to a centre shaft so that drive through the clutch is via the drum, friction faces and the centre shaft.


In signal transmission where each set of signal pulses is given a certain time or frequency slot. This allows a great number of individual signals to be carried by a common conductor.


A unit used for signal transmission where each set of signal pulses is given a certain time or frequency slot. This allows a great number of individual signals to be carried by a common conductor.


A common conductor system for digital signal transmission where each set of signal pulses carries its own unique identity. This allows a great number of individual signals to be carried by the common conductor.


A connector with more than one electrical terminal inside.

Multipoint Fuel Injection

Gasoline electronic fuel injection system with injectors in each inlet manifold spraying fuel in towards the inlet valves in the ports of each cylinder. Also known as port injection.


Sockets with many positions for fitting over a bolt or nut head. Sometimes described as multihex.

Mutual Induction

The electrical current induced in one conductor because of the electrical current flow and magnetic field produced around another conductor nearby. Used in transformers to induce a current in one winding from the electrical flow of another when both are wound around an iron core to create a magnet field.



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