Manifold Pressure/Vacuum Sensor: Description and Operation

MAP Sensor:

PURPOSE:
The Manifold Absolute Pressure (MAP) sensor is a pressure sensitive variable resistor. It measures the changes in the intake manifold pressure which result from engine load and speed changes, and converts this to a voltage output. The computer uses this voltage output to control fuel delivery and ignition timing.

The MAP sensor is also used to measure barometric pressure at start up and under certain conditions, which allows the ECM to automatically adjust for different altitudes.

OPERATION:
The ECM supplies 5 volts to the MAP sensor and monitors the voltage on a signal line. The sensor provides a path to ground through its variable resistor.

A closed throttle on engine coastdown will produce a relatively low MAP output, while a wide open throttle will produce a high output. Manifold Absolute Pressure (MAP) is the opposite of what is measured on a vacuum gauge. When manifold pressure is high, vacuum is low. A failure in the MAP sensor circuit should set Diagnostic Trouble Code (DTC) 33.