Chart C-1D Manifold Absolute Pressure (MAP) Output Check

Chart C-1D:

MAP Sensor Circuit:

CIRCUIT DESCRIPTION:

The Manifold Absolute Pressure (MAP) sensor measures the changes in the intake manifold pressure which results from engine load (intake manifold vacuum) and rpm changes; and converts these into a voltage output. The ECM sends a 5.0 volt 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 be about 1-2 volts at idle. While higher pressure (high voltage) output voltage will be about 4-4.8 volts at WOT. The MAP sensor is also used, under certain condition, to measure barometric pressure, allowing the ECM to make adjustments for different altitudes. The ECM uses the MAP sensor to control fuel delivery and ignition timing.

TEST DESCRIPTION: 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 having the same "Hot Stamped" number. See figure above. It is important that you use the same diagnostic test equipment for all measurements.

2. Applying 34 kPa (10 inches Hg) 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 leaking or restriction. Be sure no other vacuum devices are connected to the MAP hose.

NOTE: Make sure electrical connector remains securely fastened. Make sure that the MAP sensor is not hanging below the intake manifold, a false engine load could be the result of an improperly located MAP sensor.

4. Disconnect sensor from bracket and twist sensor by hand (only) to check for intermittent connection. Output changes greater than 0.10 volt indicates a bad sensor.