Circuit Description
The manifold absolute pressure (MAP) sensor responds to the pressure changes in the intake manifold. The pressure changes occur based on the engine load. The MAP sensor has a 5-volt reference circuit, a low reference circuit, and a signal circuit. The powertrain control module (PCM) supplies 5 volts to the MAP sensor on the 5-volt reference circuit. The PCM also 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. The PCM should detect a low signal voltage at a low MAP, such as during an idle or a deceleration. The PCM should detect a high signal voltage at a high MAP, such as during ignition ON, with the engine OFF, or at a wide open throttle (WOT). Certain vehicle models will also use the MAP sensor in order to determine the barometric pressure (BARO). This condition occurs when the ignition switch is turned ON, with the engine OFF. The BARO reading may also be updated whenever the engine is operated at WOT. 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, diagnostic trouble code (DTC) P0108 will set.
Conditions for Running the DTC
| • | DTCs P0121, P0122, and P0123 are not set. |
| • | The engine has been running for a period of time that is determined by the start-up coolant temperature. The 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 1,500 RPM. |
| Or |
| • | The throttle angle is less than 10 percent when the engine speed is more than 1,500 RPM. |
Conditions for Setting the DTC
The MAP sensor signal voltage is more than 4.2 volts for 7 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. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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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 shorted to voltage and should be diagnosed first. The short may be on another sensor 5-volt reference circuit.
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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 | |||||||
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 manifold absolute pressure (MAP) sensor voltage is more than the specified value? | 4.2 V | Go to Step 5 | Go to Step 4 | ||||||
Does the DTC fail this ignition? | -- | Go to Step 5 | Go to Intermittent Conditions | |||||||
5 |
Did you find and correct the condition? | -- | Go to Step 16 | Go to Step 6 | ||||||
6 |
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 9 | ||||||
7 | Measure the voltage from the 5-volt reference circuit to the low reference circuit at the MAP sensor electrical connector. Does the voltage measure within the specified value range? | 4.7-5.2 V | Go to Step 12 | Go to Step 8 | ||||||
8 | Does the voltage measure more than the specified value? | 5.2 V | Go to Step 11 | Go to Step 10 | ||||||
9 | 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 16 | Go to Step 13 | ||||||
10 | Test the low reference circuit of the MAP sensor for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 16 | Go to Step 13 | ||||||
11 |
Important: A short to voltage on the 5-volt reference circuit may also cause a MAP sensor failure. 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 16 | Go to Step 13 | ||||||
12 | 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 16 | Go to Step 14 | ||||||
13 | 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 16 | Go to Step 15 | ||||||
14 | Replace the MAP sensor. Refer to Manifold Absolute Pressure Sensor Replacement . Did you complete the replacement? | -- | Go to Step 16 | -- | ||||||
15 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 16 | -- | ||||||
16 |
Does the DTC run and pass? | -- | Go to Step 17 | Go to Step 2 | ||||||
17 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |||||||
