P0108
P0108 Manifold Absolute Pressure High Voltage
Circuit Description
The powertrain control module (PCM)/engine control module (ECM) 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 voltage outputs. The PCM/ECM 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/ECM knows the manifold pressure. A low 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/ECM to make adjustments for different altitudes.
Conditions for Setting the DTC
- No Throttle Position (TP) sensor fail conditions present.
- MAP is greater than 103 kPa.
- The TP sensor is less than 14.8% if the rpm is less than or equal to 2500.
- The TP sensor is less than 35.0% if the rpm is greater than 2500.
Action Taken When the DTC Sets
- The Malfunction Indicator Lamp (MIL) will illuminate.
- The PCM/ECM 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 Diagnostic Trouble Code (DTC) is stored.
- The PCM/ECM will substitute a fixed MAP value and use TP to control the fuel delivery (scan tool will not show defaulted 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/ECM 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 MAP Sensor Output Check for further diagnosis.
DTC P0108 may set as a result of a 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.
IMPORTANT: After repairs, use scan tool FUEL TRIM RESET function to reset long term fuel trim to 128 (0%). If DTC P0172 is also set, check the 5 volt reference circuit for a short to voltage.
Step 1 - 5:
Step 6 - 15:
Test Description
Numbers below refer to the step numbers on the Diagnostic Table.
1. The On-Board Diagnostic (OBD II) 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 malfunction occurred. The information is then stored on 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/ECM recognizes the change, the PCM/ECM, the 5 volt reference and the sensor signal circuits are OK.
5. This step also looks for an open in the sensor ground circuit. If the circuit was open, additional DTCs will also be set. If no other DTCs are set and the circuit is found to be open, then the open must be between the MAP sensor and the electrical connector ground splice.
6. When the sensor signal circuit 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.
11. The replacement PCM/ECM must be programmed. Refer to the latest Techline procedure for the PCM/ECM reprogramming.