See Figures 1 and 2
The engine computer (PCM, ECU or SBEC) 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 engine computer 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 engine computer determines atmospheric air pressure from the MAP sensor voltage. While the engine operates, the engine computer determines the intake manifold pressure from the MAP sensor voltage.
Based on MAP sensor voltage and inputs from other sensors, the engine computer adjusts spark advance and the air/fuel mixture.
On the non-Premier or Monaco 3.0L engines, the MAP sensor mounts on a bracket attached to the generator bracket. The sensor is connected to the throttle body with a vacuum hose and to the PCM electrically.
On the 3.3L and 3.8L engines, the sensor mounts to the side of the intake manifold, below the positive crankcase ventilation (PCV) valve. The sensor connects electrically to the PCM.
On all Premier and Monaco vehicles the sensor is mounted in the engine compartment on the firewall. It is connected to the throttle body with a vacuum hose and to the ECU electrically.
Except Premier and Monaco
This test should be performed with the engine cold (room temperature).
- Backprobe the dark green/red tracer wire from the MAP sensor connector with a voltmeter (do not unplug the MAP connector).
- Disconnect the vacuum hose from the map sensor and connect a vacuum pump to the sensor vacuum port.
- Place the key in the ON position, but do not start the engine.
- Apply 5 in. Hg (17 kPa) of vacuum to the sensor and record the reading on the scan tool.
While observing the scan tool, continue to slowly apply vacuum to the sensor until 20 in. Hg. (68 kPa) is reached. The voltage should decrease smoothly without any interruptions.
If the sensor does not perform as specified, replace the sensor and retest
Record the scan tool reading with 20 in. Hg of vacuum applied to the sensor. Subtract the second reading from the first reading ( i.e reading at 5 in. Hg.-reading at 20 in. Hg=difference).
If the difference is between 2.3-2.9 volts, the sensor is okay. Check the wiring and vacuum supply to the sensor.
Premier and Monaco
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 A and the positive test leads through the back of the harness connector terminal B (as marked on the sensor body). 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 ECU terminal C6 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 C with the ignition ON . The voltage should be 5 volts. Check the supply voltage at terminal C14 of the ECU. This should also be 5 volts.
- Using an ohmmeter, test the MAP sensor ground circuit at the sensor connection terminal A and at the ECU terminal D3. Repair the wire harness for an open circuit if infinite resistance is detected.
REMOVAL & INSTALLATION
See Figures 1 and 2
On the MAP sensors installed in the 3.3L and 3.8L engines, the alignment of the sensor is critical to the sensor's performance. The top of the sensor is marked "This Side Up.''
- Disconnect the negative battery cable.
- Unplug the electrical connector from the sensor.
- If so equipped, disconnect the vacuum hose from the sensor.
- Remove the MAP sensor mounting fasteners.
- Remove the sensor from the vehicle.
- Install the MAP sensor into its position and secure in place with the mounting screws. Tighten the screws until snug.
- Connect the vacuum hose, if so equipped.
- Plug the electrical connector back into the sensor. Make certain that the connector is clean and snug fitting.
- Connect the battery cable.