Manifold Pressure/Vacuum Sensor: Description and Operation

Fig. 8 Map Sensor:

MANIFOLD ABSOLUTE PRESSURE SENSOR
The Powertrain Control Module (PCM) supplies 5 volts to the MAP sensor. Intake manifold pressure is a function of barometric pressure. The MAP sensor converts 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.

During Key-On, before cranking the engine, the PCM determines atmospheric air pressure from the MAP sensor voltage. While the engine operates, the PCM determines intake manifold pressure relative to atmospheric pressure. Also, atmospheric pressure is updated at wide-open-throttle. Based on MAP sensor voltage and inputs from other sensors, the PCM adjusts spark advance and air/fuel mixture.

The MAP sensor mounts to the drivers side intake manifold plenum.

CIRCUIT OPERATION
From the Powertrain Control Module (PCM), circuit K7 supplies 5 volts to the Manifold Absolute Pressure (MAP) sensor. Circuit K7 connects to cavity A17 of the PCM connector.

Circuit K1 delivers the MAP signal to the PCM. Circuit K1 connects to cavity A27 of the PCM connector.

The PCM provides a ground path for the MAP signal (circuit K1) through circuit K4. Circuit K4 connects to cavity A4 of the PCM connector.