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Service Term to Know

MAP Sensor


The manifold absolute pressure sensor reads the amount of pressure or vacuum (also called “engine load”) in the intake manifold, where outside air is divvied up in proper amounts and distributed to each cylinder. This pressure reading is shared with the engine control module to determine how much fuel needs to be fed to each cylinder, as well as to determine ignition timing.

A fully functioning MAP sensor is necessary to maintain the right combination of acceleration, fuel economy, emissions and engine smoothness. When the throttle is wide open and air is rushing into the intake manifold (causing a drop in pressure), the MAP sensor signals the engine computer to send more fuel. When the throttle closes, pressure rises and readings from the MAP sensor tell the computer to reduce the amount of fuel going into the engine.

A faulty MAP sensor will usually trigger a “check engine” warning light. Other signs of a bad MAP sensor include rough idling, sluggish acceleration or hesitation, poor fuel economy or black smoke coming out the exhaust. Not only can the sensor fail, but vacuum hoses can develop leaks or electrical contacts can fail, triggering the warning light or causing other issues.

Some vehicles use a mass air flow sensor instead of a MAP sensor to measure the amount of air going to the intake manifold.

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