Circuit Description
The boost pressure sensor responds to pressure changes in the intake manifold. This pressure is created by the turbocharger and changes with accelerator pedal position (APP) and engine speed. The engine control module (ECM) uses this information to assist in diagnosis of the barometric pressure (BARO) sensor and to provide engine overboost protection. The boost pressure sensor has a 5-volt reference circuit, a low reference circuit, and a signal circuit. The engine control module (ECM) supplies 5 volts to the boost pressure sensor on the 5-volt reference 2 circuit, and provides a ground on a low reference circuit. The boost pressure sensor provides a signal to the ECM on a signal circuit relative to the pressure changes. The ECM monitors the boost pressure sensor signal for voltage outside of the normal range. The ECM calculates a predicted value for the boost pressure sensor. The ECM then compares the predicted value to the actual signal. This diagnostic trouble code (DTC) will set if the boost pressure sensor signal is above the predicted range.
Conditions for Running the DTC
| • | DTC P0238 is not set. |
| • | The engine is running. |
| • | The engine speed is less than 2,700 RPM. |
| • | The fuel quantity is less than 70 mm³. |
| • | The total fuel quantity burned is more than 2,000 mm³. |
Conditions for Setting the DTC
The actual boost pressure sensor signal is above the predicted range for 30 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. |
| • | The ECM limits fuel delivery. |
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
| • | Any changes to the induction system or exhaust system, such as the installation of aftermarket parts, may cause this DTC to set. |
| • | If the condition is intermittent, refer to Intermittent Conditions . |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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If the boost pressure sensor pressure is higher than the BARO pressure with the ignition ON and the engine OFF, this indicates an electrical fault.
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This step tests the wastegate actuator diaphragm for a leak.
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This step tests the wastegate actuator, the linkage, and the wastegate for proper operation.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |
2 |
Does the scan tool indicate that DTC P0108 is current? | -- | Go to DTC P0108 | Go to Step 3 |
Does the scan tool indicate that the difference between the boost sensor pressure and the BARO sensor pressure is more than the specified value? | 27 kPa | Go to Step 7 | Go to Step 4 | |
4 |
Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 5 |
Does the vacuum hold? | -- | Go to Step 6 | Go to Step 11 | |
|
Caution: Wear safety glasses when using compressed air in order to prevent eye injury. Apply compressed air, not exceeding 45 psi, to the actuator tube. Does the wastegate move to the open position? | -- | Go to Diagnostic Aids | Go to Step 11 | |
7 |
Does the test lamp illuminate? | -- | Go to Step 9 | Go to Step 8 |
8 | Test the low reference circuit of the boost sensor for high resistance or for an open. Refer to Testing for Continuity and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 10 |
9 | Inspect for poor connections at the boost 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 |
10 | Inspect for poor connections at the 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 |
11 | Replace the turbocharger. Refer to Turbocharger Replacement in Engine Mechanical. Did you complete the replacement? | -- | Go to Step 14 | -- |
12 | Replace the boost sensor. Refer to Boost 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 |
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? | -- | System OK | |
