Manifold Pressure/Vacuum Sensor: Testing and Inspection

Chart C-1D:

Wiring Diagram For MAP Sensor:

CIRCUIT DESCRIPTION:

The Manifold Absolute Pressure (MAP) sensor measures manifold pressure (vacuum) and sends that signal to the ECM. The MAP sensor is mainly used for engine load, which is an input for spark advance and fuel calculations. The MAP sensor is also used to determine the barometric pressure.


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

1. This checks MAP sensor output voltage to the ECM. This voltage, without the engine running, represents a barometer reading to the ECM. Comparing the bad BARO sensor with a known good BARO sensor, is a good way to check the accuracy of the "suspect" sensor. Readings should be within +/- .4 volts.
2. Applying 34 kPa (10" Hg.) of 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.
3. Check vacuum hose to sensor for a leak or a restriction. Be sure that no other vacuum devices are connected to the MAP sensor hose. NOTE: 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 illuminate, and for the system to set a Code 33 during this step. Be sure the code is cleared when the test is completed.