[Cliff8928]

This should help.

Originally Posted by GM

DTC P0108

Circuit Description

The manifold absolute pressure (MAP) sensor responds to pressure changes in the intake manifold. The pressure changes occur based on the engine load. The MAP sensor has the following circuits:

5-volt reference circuit
Low reference circuit
MAP sensor signal circuit
The powertrain control module (PCM) supplies 5 volts to the MAP sensor on the 5-volt reference circuit. The PCM also provides a ground on the low reference circuit. The MAP sensor provides a signal to the PCM on the MAP sensor signal circuit which is relative to the pressure changes in the manifold. The PCM should detect a low signal voltage at a low MAP, such as during an idle or a deceleration. The PCM should detect a high signal voltage at a high MAP, such as the ignition is ON, with the engine OFF, or at a wide open throttle (WOT). The MAP sensor is also used in order to determine the barometric pressure (BARO). This occurs when the ignition switch is turned ON, with the engine OFF. The BARO reading may also be updated whenever the engine is operated at WOT. The PCM monitors the MAP sensor signal for voltage outside of the normal range.

If the PCM detects a MAP sensor signal voltage that is excessively high, diagnostic trouble code (DTC) P0108 will set.

Conditions for Running the DTC

DTCs P0122 or P0123 are not set.
The throttle position is less than 12 percent.
The vehicle speed is less than 2 km/h (1 mph).
The engine run time is more than 20 to 40 seconds.

Conditions for Setting the DTC

The MAP sensor voltage is more than 3.8 volts for at least 1.25 seconds.

Action Taken When the DTC Sets

The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

Conditions for Clearing the MIL/DTC

The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
Clear the MIL and the DTC with a scan tool.

Diagnostic Aids

This DTC may set when attempting to start a vehicle that is out of fuel.
The PCM uses a single 5-volt reference output to supply power to all of the engine control components. If a component's 5 volt reference circuit is shorted to ground or shorted to voltage, the other 5-volt reference circuits may be affected.
Inspect the MAP sensor vacuum source for leaks, for restrictions, or for poor connections.
This DTC may set as the result of a misfire.
If an intermittent condition exists refer to Intermittent Conditions .