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 ECM sends a 5.0 volt reference to the MAP sensor. As the manifold pressure changes, the output voltage of the sensor also changes. By monitoring the sensor output voltage, the ECM knows the manifold pressure. 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. When comparing "Scan" tool readings to a known good vehicle, it is important to compare vehicles that use a MAP sensor having the same color insert or the same stamped number.
2. Applying 34 kPa (10" Hg.) of vacuum to the MAP sensor should cause the voltage to be 1.5 - 2.1 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.
4. Disconnect the sensor from the bracket and twist the sensor by hand (only to check an intermittent condition). Output changes greater than 0.10 volts indicate a bad sensor.

NOTE:

1. Be sure to use the same diagnostic test equipment for all measurements.
2. Make sure all electrical connections remain securely fastened.