GM Service Manual Online
For 1990-2009 cars only

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 engine control module (ECM) supplies 5 volts to the MAP sensor on the 5-volt reference circuit. The ECM provides a ground on the low reference circuit. The MAP sensor provides a signal to the ECM on the MAP sensor signal circuit which is relative to the pressure changes in the manifold. The ECM should detect a low signal voltage at a low MAP, such as during an idle or a deceleration. The ECM 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 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 TP sensor is more than 28 percent. The MAP sensor contains the following circuits:

    • A 5-volt reference
    • A low reference
    • A MAP sensor signal

If the ECM detects that the MAP sensor pressure/voltage is excessively high, DTC P0108 sets.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P0108 Manifold Absolute Pressure (MAP) Sensor Circuit High Voltage

Conditions for Running the DTC

    • DTCs P0122, P0123, P1121, and P1122 are not set.
    • The engine is running for more than 10 seconds.
    • The TP sensor is less than 15 percent if the engine speed is less than 2,500 RPM or the TP sensor is less than 35 percent if the engine speed is more than 2,500 RPM.
    • DTC P0108 runs continuously once the above conditions are met.

Conditions for Setting the DTC

The ECM detects that the MAP is more than 103 kPa for more than 5 seconds.

Action Taken When the DTC Sets

    • The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.
    • The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame/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.

Test Description

  1. This step determines if there is a short to voltage or an open condition in the circuits.

  1. This step determines if the circuit has a short to voltage. A short to voltage can cause more than 1 DTC to set.

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

Connect End View Reference: Engine Control Module Connector End Views or Engine Controls Connector End Views

1

Did you perform the Diagnostic System Check - Engine Controls?

--

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2

  1. Start the engine.
  2. Observe the DTC Information with a scan tool.

Did DTC P0108 fail this ignition?

--

Go to Step 4

Go to Step 3

3

  1. Observe the Freeze Frame/Failure Records for this DTC.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Does the DTC fail this ignition?

--

Go to Step 4

Go to Intermittent Conditions

4

  1. Turn OFF the ignition.
  2. Disconnect the manifold absolute pressure (MAP) sensor electrical connector.
  3. Turn ON the ignition, with the engine OFF.

Does the scan tool indicate that the MAP sensor parameter is less than the specified value?

12 kPa

Go to Step 5

Go to Step 7

5

Measure the voltage from the 5-volt reference circuit of the MAP sensor to a good ground.

Does the voltage measure more than the specified value?

5.2 V

Go to Step 9

Go to Step 6

6

Measure the resistance between the low reference circuit of the MAP sensor and the engine control module (ECM) housing with a DMM.

Is the resistance less than the specified value?

2 ohms

Go to Step 10

Go to Step 8

7

Test the signal circuit of the MAP sensor for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 14

Go to Step 11

8

Important: The engine control module (ECM) and MAP sensor may be damaged if the circuit is shorted to battery positive voltage.

Test the low reference circuit of the MAP sensor for the following conditions:

    • A short to voltage
    • An open
    •  High resistance

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 14

Go to Step 11

9

Important: The 5-volt reference circuits are internally and externally connected at the controller. Other sensors that share the 5-volt reference circuit may also have DTCs set. Disconnecting a sensor on the shared 5-volt reference circuit may isolate a shorted sensor. Review the electrical schematic and diagnose the shared circuits and sensors.

Test the 5-volt reference circuit of the MAP sensor for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 14

Go to Step 11

10

Test for an intermittent and for a poor connection at the MAP sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 14

Go to Step 12

11

Test for an intermittent and for a poor connection at the engine control module (ECM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 14

Go to Step 13

12

Replace the MAP sensor. Refer to Manifold Absolute Pressure Sensor Replacement .

Did you complete the replacement?

--

Go to Step 14

--

13

Replace the ECM. Refer to Engine Control Module Replacement .

Did you complete the replacement?

--

Go to Step 14

--

14

  1. Clear the DTCs with a scan tool.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

--

Go to Step 2

Go to Step 15

15

Observe the Capture Info with a scan tool.

Are there any DTCs that have not been diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List

System OK