Manifold Absolute Pressure (MAP) 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 ignition control module (ICM) adjusts spark advance and the PCM adjusts air/fuel mixture. The MAP sensor. See Fig 1 mounts to the drivers side intake manifold plenum.