For 1990-2009 cars

### Circuit Description

The manifold absolute pressure (MAP) sensor responds to changes in intake manifold pressure which gives an indication of the engine load.

The MAP sensor has:

• | A 5-volt reference circuit

• | A low reference circuit

• | A signal circuit

The powertrain control module (PCM) supplies 5 volts to the MAP sensor on the 5-volt reference circuit and provides a ground on the low reference circuit.

The MAP sensor provides a signal to the PCM on the signal circuit which is relative to the pressure changes in the manifold. With low manifold absolute pressure such as during idle or deceleration, the PCM should detect a low MAP sensor signal voltage. With high manifold absolute pressure such as ignition ON, with the engine OFF or wide-open throttle (WOT), the PCM should detect a high MAP sensor signal voltage. Certain vehicle models will also use the MAP sensor in order to calculate the barometric pressure (BARO) when the ignition is turned ON, with the engine OFF. The BARO reading may also be updated whenever the engine is operated at wide-open throttle. 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, DTC P0108 will set.

### Conditions for Running the DTC

• | DTCs P0121, P0122, or P0123 are not set.

• | The engine has been running for a length of time that is determined by the startup coolant temperature. The length of time ranges from 2 minutes at less than -30°C (-22°F) to 1 second at more than -30°C (+86°F).

• | The throttle angle is less than 2 percent when the engine speed is less than 3,000 RPM.

| OR

• | The throttle angle is less than 30 percent when the engine speed is more than 3,000 RPM.

### Conditions for Setting the DTC

The MAP sensor signal voltage is more than 4.3 volts for 3 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

• | Inspect the MAP sensor vacuum source for leaks, for restrictions, or for poor connections.

• | If the condition is intermittent, refer to Intermittent Conditions .

### Test Description

The numbers below refer to the step numbers on the diagnostic table.

1. The MAP sensor 5-volt reference circuit is shared with other sensors. If DTC P1635 is set, this indicates that the 5-volt reference circuit is either shorted to ground or shorted to voltage and should be diagnosed first. The short may be on another sensor 5-volt reference circuit.

2. Operate the vehicle within the same conditions as when the DTC failed. If you cannot duplicate the DTC, the information included in the Freeze Frame/Failure Records data can aid in locating an intermittent condition.

Step | Action | Values | Yes | No
--- | --- | --- | --- | ---
Schematic Reference: Engine Controls Schematics
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | Go to Diagnostic System Check - Engine Controls
2 |

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

Does the scan tool indicate that DTC P1635 is current?

--

Go to DTC P1635

Go to Step 3

3 | Does the scan tool indicate that the MAP sensor voltage is more than the specified value? | 4.3 V | Go to Step 5 | Go to Step 4
4 |

1. Observe the Freeze Frame/Failure Records data 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 as specified in the supporting text or as close to the Freeze Frame/Failure Records data that you observed.

Does the DTC fail this ignition?

--

Go to Step 5

Go to Diagnostic Aids

5 |

1. Turn OFF the ignition.
2. Inspect the MAP sensor and the vacuum source for the following conditions:

• | Vacuum line disconnected from the MAP sensor

• | Vacuum line pinched or cut

• | Blocked port

Did you find and correct the condition?

--

Go to Step 14

Go to Step 6

6 |

1. Disconnect the MAP sensor electrical connector.
2. Turn ON the ignition, with the engine OFF.

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

0.1 V

Go to Step 7

Go to Step 8

7 |

1. Disconnect the electrical connector of the engine coolant temperature (ECT) sensor. Refer to Engine Coolant Temperature Sensor Replacement .
2. Connect a test lamp to B+.
3. Probe the low reference circuit of the MAP sensor with the test lamp.

Does the test lamp illuminate?

--

Go to Step 10

Go to Step 9

8 | 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
9 | Test the low reference circuit of the MAP sensor for high resistance or for an open. 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 | Inspect for poor connections 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 | Inspect for poor connections at the PCM. 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 PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 14 | --
14 |

1. Use a scan tool in order to clear the DTCs.
2. Turn OFF the ignition for 30 seconds.
3. Start the engine.
4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC run and pass?

--

Go to Step 15

Go to Step 2

15 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | Go to Diagnostic Trouble Code (DTC) List | System OK