Description & Operation
The Manifold Absolute Pressure (MAP) sensor measures the pressure inside the intake manifold, by measuring the vacuum level. It sends a voltage signal to the ECM in relation to the pressure inside the manifold, which varies according to engine load and altitude. The ECM uses this signal to adjust the air/fuel ratio.
- Remove the engine cover.
- Remove the air cleaner assembly.
- Inspect the L-shaped tube from the throttle body to the MAP for cracks, blockage, and damage. Repair as necessary.
- Unplug the MAP sensor connector.
- Test the MAP sensor output voltage at the MAP sensor connector between terminals A and B. With ignition
- ON and the engine OFF, the voltage should be between 4-5 volts. If no voltage is present, proceed to Step 8.
- Test MAP sensor supply voltage at sensor connector between terminals A and C with the ignition ON and engine off, voltage should be 4.5-5.0 volts. If no voltage is present, proceed to Step 8.
- Test the MAP sensor ground circuit at terminal A of the MAP connector; voltage should be less than 0.2 volts. If not inspect for open harness from pin 4 of ECM harness and terminal A. If no voltage is present, proceed to the next step.
- Turn the ignition OFF.
- Disconnect the ECM harness from the ECM.
- Test the MAP sensor output voltage at the ECM connector. At the ECM harness connector test pin 1 of the connector, the voltage should be the same as at the MAP sensor in Step 5.
- Check ECM harness connector pin 6 for the same voltage as in Step 6.
- If all of the above tests pass, plug in ECM wiring harness and MAP sensor connector.
- With the ignition in the ON position, and the engine OFF, remove the tube from the throttle body to the MAP sensor.
- Connect a vacuum pump to the nipple on the MAP sensor, and pump the sensor to 20-27 in. Hg. of vacuum. Check the sensor output voltage, it should be below 1.8 volts. If not, replace the MAP sensor. If the voltage is OK, proceed to next step.
- Relieve vacuum pressure on the sensor, and then check the output voltage. The voltage should be 4-5 volts; if not, replace the MAP sensor.
- Install the air cleaner assembly.
Install the engine cover.