The PCM supplies 5 volts of direct current to the Manifold Absolute Pressure (MAP) sensor. The MAP sensor then converts the intake manifold pressure into voltage. The PCM monitors the MAP sensor output voltage. As vacuum increases, the MAP sensor voltage decreases proportionately. Also, as vacuum decreases, the MAP sensor voltage increases proportionally.
With the ignition key ON, before the engine is started, the PCM determines atmospheric air pressure from the MAP sensor voltage. While the engine operates, the PCM figures out intake manifold pressure from the MAP sensor voltage. Based on the MAP sensor voltage and inputs from other sensors, the PCM adjusts spark advance and the air/fuel ratio. The MAP sensor is mounted to the intake manifold, near the throttle body inlet to the manifold. The sensor connects electrically to the PCM.
- Visually check the connector, making sure it is attached properly and that all of the terminals are straight, tight and free of corrosion.
- Test the MAP sensor output voltage at the sensor connector between terminals B and C (2.4L, 3.3L and 3.8L engines), or A and B (3.0L engine).
- With the ignition switch ON and the engine not running, the output voltage should be 4-5 volts. The voltage should fall to 1.5-2.1 volts with a hot, neutral idle speed condition. If OK, go to the next step. If not OK, go to Step 5.
- Test the PCM terminal 36 for the same voltage described in the previous step to make sure the wire harness is OK. Repair as necessary.
- Test the MAP sensor ground circuit at the sensor connector terminal A (2.4L, 3.3L and 3.8L engines) or C (3.0L engine) and PCM terminal 43. If OK, go to the next step. If not OK, repair as necessary.
- Test the MAP sensor supply voltage between the sensor connector terminals A and B (2.4L, 3.3L and 3.8L engines), or A and C (3.0L engine) with the ignition key in the ON position. The voltage should be about 4.5-5.5 volts.
- There should also be 4.5-5.5 volts at terminal 61 of the PCM. If OK, replace the MAP sensor.
- If not, repair or replace the wire harness as required.