Manifold Pressure/Vacuum Sensor: Description and Operation

MAP Sensor:

PURPOSE
Informs the ECM of changes in manifold pressure (engine load).

LOCATION
On the air cleaner housing.

OPERATION
Manifold Absolute Pressure (MAP) Sensor measures changes in intake manifold pressure resulting from engine load and speed changes, and converts this to an ECM voltage input signal.

A closed throttle on deceleration produces a relatively low MAP output, while wide open throttle produces a high output. This high output is produced because pressure inside the manifold is the same as outside the manifold, resulting in a measurement of 100% of outside air pressure.

Manifold absolute pressure is OPPOSITE of engine manifold vacuum. When manifold pressure is high, vacuum is low. MAP SENSOR ALSO MEASURES BAROMETRIC PRESSURE UNDER CERTAIN CONDITIONS, ENABLING ECM TO MAKE ADJUSTMENTS FOR ALTITUDE CHANGES.

ECM sends a 5V reference signal to MAP sensor. As manifold pressure changes, electrical resistance of sensor also changes, allowing ECM to "know" manifold pressure. High pressure (low vacuum and high voltage) requires more fuel. Low pressure (high vacuum and low voltage) requires less fuel.

ECM uses MAP sensor input signal in calculations for fuel delivery and ignition timing. A failure in MAP sensor circuit should set Code 33.