Manifold Pressure/Vacuum Sensor: Description and Operation

Fig. 5 Intake Air Temperature Sensor And MAP Sensor:

OPERATION
The MAP sensor reacts to absolute pressure in the intake manifold and provides an input voltage to the PCM. The PCM interprets the MAP sensor input as engine load.

The input voltage level supplies the PCM with information relating to ambient barometric pressure during engine start-up (cranking) and engine load while its operating. The PCM uses this input along with inputs from other sensors to adjust air-fuel mixture.

The PCM supplies 5 volts direct current to the MAP sensor. The MAP sensor converts intake manifold pressure into voltage. The PCM monitors the MAP sensor output voltage. As vacuum increases, MAP sensor voltage decreases proportionately. Also, as vacuum decreases, MAP sensor voltage increases proportionately.

At key ON, before the engine is started, the PCM determines atmospheric air pressure from the MAP sensor voltage. While the engine operates, the PCM determines intake manifold pressure from the MAP sensor voltage. Based on MAP sensor voltage and inputs from other sensors, the PCM adjusts spark advance and the air/fuel mixture.

The sensor is mounted on the intake manifold Fig. 1. The sensor is connected to the throttle body or intake manifold with a vacuum hose and to the PCM electrically