For 1990-2009 cars
Engine Controls Components
Cell 23: Engine Data Sensors
OBD II Symbol Description Notice
Powertrain Control Module Connector End Views With EGR
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice

### Circuit Description

The Powertrain Control Module (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, or intake manifold vacuum, and the RPM changes, and converts these into 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, or low voltage, output voltage will be approximately 1.0 to 1.5 volts at idle. Higher pressures, or higher voltage, output voltage will be approximately 4.5 to 4.8 volts at wide open throttle (WOT). The MAP sensor is also used to measure barometric pressure, allowing the PCM to make adjustments for different altitudes.

### Conditions for Running the DTC

• | DTCs P0122 or P0123 is not set.

• | The Throttle Position (TP) sensor is less than 12%.

• | The vehicle speed sensor is less than 2 km/h (1 mph).

• | The engine run time is greater than 20 to 40 seconds.

### Conditions for Setting the DTC

• | The MAP sensor is greater than 82 kPa.

• | The above conditions are met for at least 1.25 seconds.

### Action Taken When the DTC Sets (With EGR)

• | 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.)

• | The vehicle will operate in Open Loop when the vehicle is under 8 km/h (5 mph). The vehicle will operate in Closed Loop when the vehicle is over 8 km/h (5 mph).

### Action Taken When the DTC Sets (Without EGR)

• | The Malfunction Indicator Lamp (MIL) will illuminate afer two consecutive ignition cycles in which the diagnostic runs with the fault active.

• | 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.)

• | The vehicle will operate in Open Loop when the vehicle is under 8 km/h (5 mph). The vehicle will operate in Closed Loop when the vehicle is over 8 km/h (5 mph).

### 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.

• | The MIL/DTCs can be cleared by using the scan tool.

### Diagnostic Aids

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

With the ignition switch 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 + or - 0.4 volt.

If a DTC P0108 is intermittent, refer to Symptoms or to the Manifold Absolute Pressure Sensor Output Diagnosis for further diagnosis.

The 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.

If a DTC P0172 is also set, check the 5.0 volt reference circuit for a short to voltage.

### Test Description

The numbers below refer to the step numbers on the Diagnostic Table.

1. The Powertrain OBD System Check prompts you to complete some of the basic checks and to store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data captured when the malfunction occurred. The scan tool stores this data for later reference.

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

3. This step simulates the conditions for a DTC P0107. If the PCM recognizes the change, the PCM, the 5.0 volt reference and the MAP sensor signal circuits are OK.

4. This step looks for an open in the MAP sensor ground circuit.

5. When the MAP sensor signal circuit is shorted to battery voltage, the TP will display above 0 percent at all times and the A/C High Side will display high. The vehicle will also remain in Open Loop.

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

7. Important: The Powertrain Control Module (PCM) uses a single internal 5.0 volt power supply to supply power to all the engine control components. If one component shorts its 5.0 volt reference circuit to ground or battery voltage, the other 5.0 volt reference circuits will also have a low or high voltage.

   Disconnect all of the sensors that use a 5.0 volt reference one at a time while monitoring the short on the 5.0 volt reference circuit. Replace any sensor that may have caused the short on the 5.0 volt reference circuit.

8. Reprogram the replacement PCM and perform the crankshaft position system variation learn procedure. Refer to the latest Techline information for PCM programming and Crankshaft Position System Variation Learn for the crankshaft position system variation learn procedure.

#### DTC P0108-Manifold Absolute Pressure (MAP) Circuit-High Voltage

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | Go to Step 2 | Go to Powertrain On Board Diagnostic (OBD) System Check
2 |

1. Install a scan tool.
2. Start the engine.
3. Idle the engine.

Does the scan tool display a MAP voltage of the specified value or more?

4.0 V

Go to Step 3

Go to Step 4

3 |

1. Turn OFF the ignition switch.
2. Disconnect the MAP sensor electrical connector.
3. Turn ON the ignition switch leaving the engine OFF.

Does the scan tool display a MAP voltage of the specified value or less?

1.0 V

Go to Step 5

Go to Step 6

4 |

1. Turn ON the ignition switch leaving the engine OFF.
2. Review the Freeze Frame data and record the parameters.
3. Start the engine.
4. Operate the vehicle within the freeze frame conditions and Conditions For Running The DTC as specified in the supporting text.

Does the scan tool display a MAP voltage of the specified value or more?

4.0 V

Go to Step 3

Go to Diagnostic Aids

5 |

1. Connect a test light to battery voltage.
2. Probe the MAP sensor ground circuit terminal.

Does the test light illuminate?

--

Go to Step 7

Go to Step 11

6 |

1. Turn OFF the ignition switch.
2. Check the MAP sensor signal circuit for a short to voltage.
3. Repair the circuit as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

--

Go to Step 14

Go to Step 12

7 |

1. Connect a DMM to ground.
2. Probe the 5.0 volt reference circuit.

Does the DMM display near the specified value?

5.0 V

Go to Step 8

Go to Step 9

8 |

1. Turn OFF the ignition switch.
2. Check the MAP sensor vacuum source for the following conditions:

• | Plugged

• | Leaking

Was a problem found?

--

Go to Step 10

Go to Step 13

9 | Important: The Powertrain Control Module (PCM) uses a single internal 5.0 volt power supply to supply power to all the engine control components. If one component shorts its 5.0 volt reference circuit to ground or battery voltage, the other 5.0 volt reference circuits will also have a low or high voltage.

1. Turn OFF the ignition switch.
2. Check the 5.0 volt reference circuit for a short to battery voltage.
3. Repair the circuit as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

--

Go to Step 14

Go to Step 12

10 | Repair the vacuum source as necessary. Is the action complete? | -- | Go to Step 14 | --
11 |

1. Turn OFF the ignition switch.
2. Check for the following conditions in the MAP sensor ground circuit:

• | Open circuit

• | Poor electrical terminal connection(s)

3. Repair the circuit as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

--

Go to Step 14

Go to Step 12

12 | Replace the PCM. Refer to the Powertrain Control Module Replacement . Is the action complete? | -- | Go to Step 14 | --
13 |

1. Turn OFF the ignition switch.
2. Check for a poor ground terminal connection at the MAP sensor electrical connection.
3. If terminal connection is OK, then replace the MAP sensor. Refer to the Manifold Absolute Pressure Sensor Replacement .

Is the action complete?

--

Go to Step 14

--

14 |

1. Using the scan tool, clear the DTCs.
2. Start the engine.
3. Idle the engine at the normal operating temperature.
4. Operate the vehicle within the conditions for running this DTC as specified in the supporting text.

Does the scan tool indicate that this diagnostic ran and passed?

--

Go to Step 15

Go to Step 2

15 | Check to see if any additional DTCs are set. Does the scan tool display any DTCs that you have not diagnosed? | -- | Go to applicable DTC table | System OK