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 Powertrain Control Module (PCM) to automatically adjust for different altitudes.

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 PCM to automatically adjust to different altitudes. The PCM 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 PCM 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 or DTC 34.