Manifold Pressure/Vacuum Sensor: Description and Operation

MAP Sensor:

PURPOSE
The Manifold Absolute Pressure (MAP) sensor is a pressure sensor that measures changes in intake manifold pressure. The pressure changes as a result of engine load and speed. The MAP sensor converts this to a voltage output.

OPERATION
A closed throttle on engine coastdown would produce a relatively low MAP voltage output, while a wide open throttle would produce a high voltage output. Manifold absolute pressure is the OPPOSITE of vacuum. When manifold pressure is high, vacuum is low. The MAP sensor is also used to measure barometric pressure under certain conditions, which allows the ECM to automatically adjust to different altitudes. The ECM sends a 5 volt reference signal to the MAP sensor. As manifold pressure changes, electrical resistance of the sensor also changes. By monitoring the sensor output voltage, the ECM knows the manifold pressure. A high pressure, low vacuum (high voltage) condition requires more fuel, while a low pressure, high vacuum (low voltage) requires less fuel.

A fault in the MAP sensor circuit should set a Diagnostic Trouble Code (DTC) 33.