Manifold Pressure/Vacuum Sensor: Testing and Inspection

Chart C-1D:

MAP Sensor Wiring Circuit:

CIRCUIT DESCRIPTION:
The Manifold Absolute Pressure (MAP) sensor measures the change in the intake manifold pressure which result from engine load (intake manifold vacuum) and rpm changes and converts these into a voltage output.

The ECM sends a 5 volts reference voltage 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. A lower pressure (low voltage) output voltage will he about 1 to 2 volts at idle. While higher pressure (high voltage) output voltage will be about 4 to 4.8 at Wide Open Throttle (WOT). The MAP sensor is also used, under certain conditions, to measure barometric pressure, allowing the ECM to make adjustments for altitude changes. The ECM uses the MAP sensor to control fuel delivery and ignition timing.

TEST DESCRIPTION: Number(s) below refer to circled number(s) on the diagnostic chart.

NOTE: Be sure to use the same diagnostic test equipment for all measurements.

1. When comparing scan readings to a known good vehicle, it is important to compare vehicles that use a MAP sensor having the same color insert and the same "hot Stamped" number. Refer to Figures 1 and 2 on chart.
2. Applying 34 kPa (10" Hg) vacuum to the MAP sensor should result in voltage readings of 1.5 to 2.1 volts less than the voltage in 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 seal to sensor for leaking or restriction.

NOTE: Make sure electrical connector remains securely fastened.

4. Remove sensor from the intake plenum and twist sensor (by hand only) to check for intermittent connection. Output changes greater than .10 volt indicate a faulty sensor or connection. If OK, replace sensor.