The PCM supplies 5 volts to the Manifold Absolute Pressure (MAP) sensor. The MAP sensor converts what it reads as the amount of intake manifold pressure into a return signal. The PCM monitors the MAP sensor output voltage. As vacuum increases in the intake manifold, the MAP sensor voltage decreases proportionately. Also, as vacuum decreases, the MAP sensor voltage increases proportionately.
During engine cranking, before the engine starts running, the PCM determines atmospheric air pressure from the MAP sensor voltage. While the engine operates, the PCM determines the 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.
See Figures 1, 2, 3 and 4
Before testing any electrical component, inspect the wiring and connectors for damage. Also wiggle the connectors to ensure a that they are firmly engaged. When testing the sensor, use a high input impedance digital volt-ohmmeter. Insert the tester leads through the back of the connector. Do not disconnect the electrical harness.
- Inspect the vacuum hose connections at the sensor and throttle body. Repair or replace the hoses, if any hoses are cracking or vacuum is leaking.
For the following step, do not unplug the sensor connector-it must stay plugged in.
- Make sure that the sensor wiring connector is fully inserted into the sensor (loose connections can create trouble codes). Check the MAP sensor output voltage by inserting the negative lead of a voltmeter into the back of terminal 2 and the positive test leads through the back of the harness connector terminal 3 (as marked on the sensor body). Refer to the accompanying wiring illustration. With the ignition switch in the ON position and the engine OFF , the output voltage should be 4-5 volts.
- Start the engine and allow to idle at normal operating temperature. The output voltage should drop to 1.5-2.1 volts.
- Test the PCM terminal 36 (1993-95 models), and terminal 1 (1996-97 models) for the same voltage described above to verify the wire harness condition. Repair the wiring harness if the voltage is not the same.
- Test the MAP sensor supply voltage at the sensor connection terminal 2 and 1 with the ignition ON . The voltage should be 5 volts. Check the supply voltage at terminal 61 of the PCM. This should also be 5 volts.
- Using an ohmmeter, test the MAP sensor ground circuit at the sensor connection terminal 1 and at the PCM terminal 43 (1993-95 models), terminal 4 (1996-97 models). Repair the wire harness for an open circuit if infinite resistance is detected.
REMOVAL & INSTALLATION
See Figures 5 and 6
The MAP sensor is located in the rear of the intake manifold plenum on the 3.3L engine. On the 3.5L engine, the MAP sensor is threaded into the left side of the intake manifold plenum.
- Disconnect the negative battery cable.
- Unplug the electrical connector from the sensor.
- Remove the MAP sensor mounting screws.
- Remove the sensor from the vehicle.
- Install the MAP sensor into its position and secure in place with the mounting screws. Tighten the screws to 90 inch lbs. (10 Nm), then rotate it to a horizontal position.
- Plug the electrical connector back into the sensor. Make certain that the connector is clean and snug fitting.
- Connect the negative battery cable.