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DTC P0234 or P0299 (LBY)

DTC P0234 or P0299 (LBY)

Diagnostic Instructions


• Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• Diagnostic Procedure Instructions provides an overview of each diagnostic category.


DTC Descriptors

DTC P0234 00

Engine Overboost

DTC P0299 00

Engine Underboost

Circuit/System Description

The turbocharger pressure sensor responds to pressure changes in the intake manifold. The pressure changes occur based on the engine load, and turbocharger boost. The engine control module (ECM) supplies 5 V to the turbocharger pressure sensor on the 5 V reference circuit. The ECM provides a ground on the low reference circuit. The turbocharger pressure sensor provides a signal to the ECM on the signal circuit which is relative to the pressure changes in the manifold.

Conditions for Running the DTC


• The engine is running.

• The DTCs run continuously when the above conditions are met.


Conditions for Setting the DTC

P0234 00

The actual turbocharger boost pressure is greater than the desired range for greater than 6 s.

P0299 00

The actual turbocharger boost pressure is less than the desired range for greater than 6 s.

Action Taken When the DTC Sets

DTCs P0234 and P0299 are Type B DTCs.

Conditions for Clearing the DTC

DTCs P0234 and P0299 are Type B DTCs.

Reference Information

Schematic Reference

Engine Controls Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Turbocharger System Description

Electrical Information Reference


• Circuit Testing

• Connector Repairs

• Testing for Intermittent Conditions and Poor Connections

• Wiring Repairs


DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

Special Tools

EN 23738-A Mityvac

For equivalent regional tools, refer to Special Tools .

Circuit/System Verification


1. Ignition ON, compare the scan tool Boost Pressure Sensor parameter to the barometric pressure (BARO) parameter. Both parameters should be within 5 kPa (0.72 PSI).

2. If not within the specified range, refer to Diagnostic Trouble Code (DTC) List - Vehicle for further diagnosis.

3. Observe the DTC information with a scan tool. Verify that DTC P0045, P0047, or P0048 are not set.

4. If any of the DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle for further diagnosis.

5. Engine running, increase the engine speed to 2000 rpm. Change parameter for charge pressure actuator LPT between ON and OFF with the scan tool. Verify the scan tool Boost Pressure Sensor parameter increases and decreases with the scan tool commands.

6. Engine running, increase the engine speed to 2000 rpm. Change parameter for charge pressure actuator HPT between ON and OFF with the scan tool. Verify the scan tool Boost Pressure Sensor parameter increases and decreases with the scan tool commands.

7. Operate the vehicle within the conditions for running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.


Circuit/System Testing


1. Inspect the fuel tank for the right fuel content

2. Inspect the intake, and the exhaust systems, for the following:

• Leaks or restrictions

• Damaged or missing components

• Aftermarket components

3. If a condition is found, repair as necessary.

4. Disconnect the vacuum source from the M91A Boost Pressure Actuator LPT.

5. Connect the EN 23738-A Mityvac to the M91A Boost Pressure Actuator LPT vacuum supply hose. Engine running, verify the vacuum is greater than -50 kPa (-7.25 PSI).

6. If less than the specified range, inspect the vacuum supply hose and filter for a leak or restriction. If the supply hose is normal, replace the vacuum pump.

7. Connect the vacuum source to the M91A Boost Pressure Actuator LPT. Connect the EN 23738-A Mityvac to the M91A Boost Pressure Actuator LPT vacuum port. Engine running, command the M91A Boost Pressure Actuator LPT to 5% with a scan tool. Verify the vacuum is between 0 to -40 kPa (0-5.8 PSI).

8. If greater than the specified range, replace the M91A Boost Pressure Actuator LPT.

9. Command the M91A Boost Pressure Actuator LPT ON with a scan tool. Verify the vacuum is greater than -50 kPa (-7.25 PSI).

10. If less than the specified range, replace the M91A Boost Pressure Actuator LPT.

11. Connect the EN 23738-A Mityvac to the M91A Boost Pressure Actuator LPT vacuum actuator hose. Apply -50 kPa (-7.25 PSI) vacuum, verify the Turbocharger By Pass rod is moving.

12. If less than the specified range, inspect the vacuum hose for a leak or restriction. If the supply hose is normal, replace the M91A Boost Pressure Actuator LPT vacuum actuator.

13. Disconnect the vacuum source from the M91B Boost Pressure Actuator HPT.

14. Connect the EN 23738-A Mityvac to the M91B Boost Pressure Actuator HPT vacuum supply hose. Engine running, verify the vacuum is greater than -50 kPa (-7.25 PSI).

15. If less than the specified range, inspect the vacuum supply hose and filter for a leak or restriction. If the supply hose is normal, replace the vacuum pump.

16. Connect the vacuum source to the M91A Boost Pressure Actuator LPT. Connect the EN 23738-A Mityvac to the M91B Boost Pressure Actuator HPT vacuum port. Engine running, command the M91B Boost Pressure Actuator HPT to 5% with a scan tool. Verify the vacuum is between 0 to -40 kPa (0-5.8 PSI).

17. If greater than the specified range, replace the M91B Boost Pressure Actuator HPT.

18. Command the M91B Boost Pressure Actuator HPT ON with a scan tool. Verify the vacuum is greater than -50 kPa (-7.25 PSI).

19. If less than the specified range, replace the M91B Boost Pressure Actuator HPT.

20. Connect the EN 23738-A Mityvac to the M91B Boost Pressure Actuator HPT vacuum actuator hose. Apply -50 kPa (-7.25 PSI) vacuum, verify the Turbocharger By Pass rod is moving.

21. If less than the specified range, inspect the vacuum hose for a leak or restriction. If the supply hose is normal, replace the M91B Boost Pressure Actuator HPT vacuum actuator.

22. Inspect the turbocharger oil supply lines for a restriction.

23. If restricted, repair or replace as necessary.

24. If all other components test normal, replace the turbocharger.


Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.


• Vacuum Pump Assembly Replacement

• Turbocharger Replacement (LBY/A20DTR) Turbocharger Replacement (LBS/A20DTH)

• Engine Control Module Replacement for ECM replacement, setup, and programming