MAP Sensor Circuit Diagnosis

Circuit Description

The Manifold Absolute Pressure (MAP) sensor responds to changes in intake manifold pressure (vacuum). The MAP sensor signal voltage to the PCM varies from below 2.0 volts at idle (high vacuum) to above 4.0 volts with the key on, engine not running, or engine running at wide open throttle (low vacuum). The MAP sensor is used to determine manifold pressure changes while the linear EGR flow test diagnostic is being run to determine engine vacuum level for other diagnostics and to determine barometric pressure (BARO). The PCM monitors the MAP signals for voltages outside the normal range of the MAP sensor. If the PCM detects a MAP signal voltage that is excessively high, DTC P0108 Manifold Absolute Pressure (MAP) Sensor Circuit High Voltage will be set. If the PCM detects a MAP signal voltage that is excessively low, DTC P0107 Manifold Absolute Pressure (MAP) Sensor Circuit Low Voltage will be set.

The PCM also uses the MAP Sensor for throttle position sensor performance. If the PCM detects a TP in an out of range condition, when the MAP reading is above or below a calibrated amount then DTC P0121 Throttle Position (TP) Sensor Performance will be set.

Diagnostic Aids

Check for the following conditions:

^ Monitor the MAP sensor using the scan tool. If the MAP sensor does not respond to throttle changes, check the 3X reference circuits from the ignition control module to the PCM.
If the 3X reference signal is lost the PCM will only update the MAP sensor reading once per key cycle, when the engine is first started. Depending on where the MAP sensor voltage (high voltage or low voltage) is when the engine is started, the high or low voltage MAP sensor DTCs will set.
^ Inspect for kinked and damaged vacuum hoses, ensure that a good vacuum source is available. Refer to Emission Hose Routing Diagram in Emission Control Systems.

Important: Remove any debris from the connector surfaces before servicing a component. Inspect the connector gaskets when diagnosing or replacing a component. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion.

^ Poor terminal connection.
Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and faulty terminal to wire connection. Use a corresponding mating terminal to test for proper tension. Refer to Diagrams.
^ Damaged harness.
Inspect the wiring harness for damage. If the harness appears to be OK, observe the sensor display on the scan tool while moving connectors and wiring harnesses related to the sensor. A change in the sensor display may indicate the location of the fault.
^ Inspect the PCM and the engine grounds for clean and secure connections.

If the DTC is determined to be intermittent, reviewing the Fail Records can be useful in determining when the DTC was last set.