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Malfunction Indicator Lamp (MIL)

This amber dashboard warning light may be labeled "check engine" or "service engine soon".

Malleability

The ability of a metal to be formed through hammering or bending.

Manganese

An element (Mn), used in alloys of iron, steel, aluminum, and copper, often confused with magnesium (Mg).

Manganese Bronze

An alloy of copper, zinc, and up to 3.0% manganese used for toothed wheels and gears.

Manganese Steel

A steel alloy with 12-14% manganese; used for drill bits.

Manifold

1. A device used to hold two or more gauges with fluid passages and flow provisions; used for testing ans servicing purposes. 2. A conduit-like device used to channel the air/fuel mixture into an engine. 3. A conduit-like device used to duct the exhaust gas out of an engine.

Manifold Absolute Pressure (MAP)

The pressure in an intake manifold relative to atmospheric pressure.

Manifold Absolute-Pressure Sensor

A variable resistor used as a sensor to signal an engine-control computer relative to the vacuum conditions in the intake manifold.

Manifold Air Temperature

The temperature of the intake stream in the intake manifold, as increased by a heat riser or an Early Fuel-Evaporation system, and/or converted to an engine-control computer input by a sensor.

Manifold Gauge Set

1. A set of gauges used to service an air-conditioning system. 2. A set of gauges used to measure vacuum or pressure in an engine's intake or exhaust system.

Manifold Heat Control

A flapper-type valve in the exhaust manifold that diverts heat to the intake manifold.

Manifold Pressure

A positive pressure in the intake manifold measured in pounds per square inch or bars.

Manifold Vacuum

The negative pressure in an engine's intake manifold produce by the engine's pumping action and measured in inches of mercury.

Manomometer (u-tube)

A u-shaped tube with a graduated scale used for measuring the pressure of gases or vapors.

Manual Bleeding

A two-technician technique for bleeding brakes; one pumps the brakes as the other opens and closes the bleeder screws when required.

Manual Control Valve

A spool valve, located in the valve body, that determines fluid flow from the valve body to various hydraulic circuits controlled by the vehicle driver through the selector lever.

Manual Low

The position of the units in an automatic transmission when the driver selects the Low or first-gear position of the quadrant.

Manual Operation

1. The act of operating the power steering system in the event of an engine system failure; increased effort is required. 2. The ability to override or cancel any automatic or semi-automatic function.

Manual Selection

The vehicle operator's ability to 1. Move the gear selector lever by hand, such as with a manual transmission. 2. Select any condition or function using a keypad, switch or lever.

Manual Slide Release

The release mechanism for a sliding fifth wheel, which is operated by hand.