Manifold Pressure/Vacuum Sensor: Description and Operation

PCM Wiring:

PURPOSE
The Manifold Absolute Pressure (MAP) sensor is mounted inside of the intake manifold and measures the changes in intake manifold pressure which result from engine speed and load changes. The MAP sensor is also used to calculate barometric pressure under certain vehicle conditions. This eliminates the need for a separate Barometric (BARO) sensor. By monitoring the sensor output voltage, the PCM can calculate the manifold pressure, and increase or decrease the injector duration to allow for the addition or reduction of fuel. The PCM also uses the MAP sensor to control ignition timing.


DESCRIPTION
The sensor converts a pressure input to a voltage output. The MAP sensor output voltage signal is directly related to pressure (kPa). A high pressure (atmospheric pressure) will produce an output of about 4.5 to 5.0 volts. A low pressure will produce about 0.5 to 0.9 volts. Manifold absolute pressure is the opposite of what you would measure with a vacuum gauge. When manifold pressure is high, vacuum is low.

As the manifold pressure changes, the electrical output of the sensor also changes. A higher pressure (low vacuum) requires more fuel, while a lower pressure (higher vacuum) requires less fuel. A failure in the MAP sensor circuit should set a code P031, P032, or P034. An intermittent problem can set a code P071.


LOCATION
The MAP sensor is mounted inside of the intake manifold, on the top LH side of engine.