The MAP sensor is attached to the plenum chamber near the hood latch. It reacts to absolute pressure in the intake manifold and provides an input voltage to the ECU. Manifold pressure is used to supply mixture density information and ambient barometric pressure information that is necessary for computing the air/fuel mixture. A vacuum line from the throttle body attaches to the MAP sensor to provide its input pressure. A Manifold Air Temperature (MAT) sensor is located in the intake manifold and measures the air/fuel mixture temperature to allow the ECU to compensate for air density changes during high temperature operation.
See Figure 1
- Inspect the MAP sensor vacuum hose connections at the throttle body and sensor and repair as necessary.
- Test the MAP sensor output voltage at the MAP sensor connector terminal B as marked on the sensor body, with the ignition switch ON (engine OFF). The output voltage should be 4-5 volts.
- Test ECU terminal 33 for the same voltage described above to verify the wire harness condition. Repair as necessary.
- Test the MAP sensor supply voltage at the sensor connector terminal C with the ignition ON . It should be 4.5-5.5 volts. This voltage should also be at terminal 16 of the ECU wire harness connector. Repair or replace the wire harness as necessary. Test the ECU with Diagnostic Tester MS 1700, if necessary.
- Test the MAP sensor ground circuit at sensor connector terminal A and ECU connector terminal 17. Repair the wire harness, if necessary.
- Test the MAP sensor ground circuit at the ECU connector between terminal 17 and terminal 2 with an ohmmeter. If the ohmmeter indicates an open circuit, inspect for a defective sensor ground connection on the flywheel/drive plate housing near the starter motor. If the ground connection is good, replace the ECU. If terminal 17 has a short circuit to 12 volts, correct this condition before replacing the ECU.
REMOVAL & INSTALLATION
See Figure 2
- Unplug the MAP sensor electrical connector.
- Disconnect the MAP sensor vacuum supply hose.
- Remove the MAP sensor mounting nuts and remove the map sensor.
- Installation is the reverse of removal.