MAP Sensor Output Diagnosis

Circuit Description
The Manifold Absolute Pressure (MAP) sensor measures the changes in the intake manifold pressure which result from the engine load (intake manifold vacuum) and the RPM changes then converts these into a voltage output. The Powertrain Control Module (PCM) supplies a 5 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 PCM knows the manifold pressure. A lower pressure (low voltage) output voltage will be about 1.0 to 1.5 volts at idle. While high pressure (high voltage) output voltage will be about 4.5 to 4.8 volts at Wide Open Throttle (WOT). The MAP sensor is also used, under certain conditions, to measure barometric pressure, allowing the PCM to make adjustment for different altitudes. The PCM uses the MAP sensor in order to control the fuel delivery and the ignition timing.

Test Description
The numbers below refer to the step numbers on the Diagnostic Table.

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

4. Applying 34 kPa (10 in of Hg) vacuum to the MAP sensor should cause the voltage to be 1.5 to 2.1 volts less than the voltage at Step 3. Upon applying vacuum to the sensor, the change in voltage should be instantaneous. A slow voltage change indicates a malfunctioning sensor.
6. Check vacuum hose to sensor for leaking or restriction. Be sure that no other vacuum devices are connected to the MAP hose.

Important: Make sure electrical connector remains securely fastened.

7. Move sensor electrical connector by hand only while watching scan tool to check for intermittent connection. Output changes more than 0.10 volt indicate a bad connection. If OK, replace sensor.