Manifold Pressure/Vacuum Sensor: Testing and Inspection

Chart C-1D Manifold Absolute Pressure Voltage Output Check:

MAP Sensor Wiring Diagram:

CIRCUIT DESCRIPTION:

The manifold absolute pressure sensor (MAP) measures manifold pressure (vacuum) and then sends that signal to the ECM. The MAP sensor is mainly used for fuel calculation and when the ECM is running in the throttle body back-up mode. The ECM uses the MAP sensor to control fuel delivery and igniting timing.

TEST DESCRIPTION: Numbers below refer to circled numbers on the diagnostic chart.

1. Checks MAP sensor output voltage to the ECM. This voltage, without engine running, represents a barometer reading to the ECM.

2. Applying 34 kPa (10 inches Hg) vacuum to the MAP sensor should cause the voltage to be 1.2 volts less than the voltage at Step 1. Upon applying vacuum to the sensor, the change in voltage should be instantaneous. A slow voltage change indicates a faulty sensor. The engine must be running in this step or the SCAN tool will not indicate a change in voltage. It is normal for the "SERVICE ENGINE SOON" light to come "ON" and for the system to set a Code 33 during this step. Make sure the code is cleared after test is completed.

3. Check vacuum hose to sensor for leaking or restriction. Be sure no other vacuum devices are connected to the MAP hose.

4. Disconnect sensor from the bracket and twist by hand to check for intermittent connection. Output changes greater than 0.10 volt indicate a bad sensor.