Manifold Pressure/Vacuum Sensor: Testing and Inspection

Manifold Absolute Pressure (MAP) Sensor Circuit:

Circuit Description
The Manifold Absolute Pressure (MAP) sensor measures the changes in the intake manifold pressure which result from engine load (intake manifold vacuum) and RPM changes. The Powertrain Control Module (PCM) sends 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 higher 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 adjustments for different altitudes. The PCM uses the MAP sensor to control fuel delivery and ignition timing.

Manifold Absolute Pressure (MAP) Sensor Output Check:

Test Description
Numbers below refer to the step numbers on the Diagnostic Table.
1. The On Board Diagnostics (OBD) System Check prompts the technician to store the Freeze Frame Data in the scan tool. This will create an electronic copy of the freeze frame data taken when the fault occurred that can be referred to later.
4. Applying 34 kPa (10"Hg) vacuum to the MAP sensor should cause the voltage to be 1.5 to 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.
6. Check vacuum source to sensor for leakage or restrictions. Do not connect other vacuum devices to the MAP sensor hose.
7. Move the MAP sensor electrical connector by hand (only) while watching scan tool for an intermittent connection. Output changes greater than 0.10 volt indicate a bad connection.