P0108

Diagnostic Chart:

Wiring Diagram:

CIRCUIT DESCRIPTION

The PCM uses the Manifold Absolute Pressure (MAP) sensor to control the fuel delivery and the ignition timing. The MAP sensor measures the changes in the intake manifold pressure which results from engine load (intake manifold vacuum) and the RPM changes; and converts these into a voltage outputs. 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 MAP sensor also changes. By monitoring the MAP 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 pressures (high voltage) output voltage will be about 4.5 to 4.8 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.

CONDITIONS FOR SETTING THE DTC

^ MAP is greater than 82 kPa.

^ Throttle Position (TP) sensor is less than 12 %.

^ Vehicle speed is less than 1 mph (2 km/h).

^ Above conditions met for 10 seconds.

^ Engine has run for at least 20-40 seconds.

^ DTC(s) P0122 or P0123 not set.

ACTION TAKEN WHEN THE DTC SETS

^ The Malfunction Indicator Lamp (MIL) will illuminate.

^ The Powertrain Control Module (PCM) will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame and Failure Records buffers.

^ A history DTC is stored.

^ Coolant fan turns ON.

^ The PCM will substitute a fixed MAP value and use Throttle Position (TP) to control the fuel delivery (scan tool will not show defaulted value 0.

CONDITIONS FOR CLEARING THE MIL/DTC

^ The MIL will turn OFF after three consecutive ignition cycles in which the diagnostic runs without a fault.

^ A history DTC will clear after 40 consecutive warm up cycles without a fault.

^ DTC(s) can be cleared by using the scan tool.

DIAGNOSTIC AIDS

With the ignition ON and the engine stopped, the manifold pressure is equal to atmospheric pressure and the signal voltage will be high.

This information is used by the PCM as an indication of vehicle altitude. Comparison of this reading with a known good vehicle with the same sensor is a good way to check the accuracy of a suspect sensor. Readings should be the same ±0.4 volt.

If a DTC P0108 is intermittent, refer to Symptoms or to MAP Sensor Output Check for further diagnosis. Testing and Inspection MAP Sensor Output Diagnosis

DTC P0108 may set as a result of misfire. If misfire is present, repair the cause of misfire before using this table. The misfire counters may be used to determine which cylinder(s) is misfiring.

NOTE:: After repairs, use scan tool Fuel Trim Reset function to reset long term fuel trim to 128 (0%).

If a DTC P0172 and DTC P1406 are also set, check the 5 volt reference circuit for a short to voltage.

TEST DESCRIPTION

Number(s) below refer to the step number(s) on the Diagnostic Table.

1. The Powertrain OBD System Check prompts the technician to complete some basic checks and store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.

2. This step will determine if DTC P0108 is the result of a hard failure or an intermittent condition.

3. This step simulates conditions for a DTC P0107. If the PCM recognizes the change, the PCM and CKT 416 and 01Cr 432 are OK.

5. This step looks for an open CKT 469. If the circuit was open, additional DTC's will also be set. If no other DTC(s) are set and the circuit is found to be open, then the open must be between the MAP sensor and the electrical connector sensor ground splice.

6. When CKT 432 is shorted to battery voltage, the TP will be displayed above 0% at all times and A/C High Side will be displayed high. The vehicle will also remain in Open Loop.

8. The MAP sensor vacuum source should only supply vacuum to the MAP sensor. Check the vacuum port for a restriction caused by casting flash.

9. Disconnect all sensors that use a 5 volt reference one at a time while monitoring the short on the 5 volt reference circuit. Replace any sensor that may have caused the short on the 5 volt reference circuit.