Buick Regal: DTC P0234 or P0299

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

Engine Overboost

DTC P0299

Engine Underboost

Circuit Description

The boost pressure sensor is integrated with the intake air temperature (IAT) sensor 3. The boost pressure sensor measures the range of pressures between the turbocharger and the throttle body. The sensor used on this engine is a three atmosphere sensor. Pressure in this portion of the induction system is affected by engine speed, throttle opening, turbocharger boost pressure, IAT, barometric pressure (BARO), and the efficiency of the charge air cooler.

The sensor provides a signal voltage to the engine control module (ECM), relative to the pressure changes, on the boost pressure signal circuit. Under normal operation the greatest pressure that can exist in this portion of the induction system at ignition On, engine Off is equal to the BARO. When the vehicle is operated at wide-open throttle (WOT) the turbocharger can increase the pressure to near 240 kPa (34.8 psi). The lowest pressure that occurs is when the vehicle is idling or decelerating, and it is equal to BARO.

Conditions for Running the DTCs

• DTC P0010, P0011, P0013, P0014, P0016, P0017, P0033, P0034, P0035, P0068, P00C8, P00C9, P0111, P0112, P0113, P0114, P0116, P0122, P0123, P0128, P0222, P0223, P0236, P0237, P0238, P0243, P0245, P0246, P0601, P0604, P0606, P1682, P16A0, P16A1, P16F3, P2101, P2176, P2227, P2228, P2229, P2230 or P2261 is not set.
• The driver requested boost pressure level exceeds the level of the base boost pressure.
• The engine speed is between 1, 600 - 6, 000 RPM.

  The desired boost pressure is between 140 - 300 kPa (20.3 - 43.5 psi) The Barometric Pressure (BARO) is between 60 - 120 kPa (8.7 - 17.4 psi).

  The Engine Coolant Temperature (ECT) is between -40 to +120ºC (-40 to +248ºF).

  The Intake Air Temperature (IAT) is between -40 to +80ºC (-40 to +176ºF) The turbocharger wastegate is not under output device control.

  The turbocharger bypass valve is not under output device control.

  The DTCs run continuously when the above conditions have been met.

Conditions for Setting the DTC

P0234

The ECM detects that the actual boost pressure is greater than the desired boost pressure by a calibrated amount for greater than 3 s.

P0299

The ECM detects that the actual boost pressure is less than the desired boost pressure by a calibrated amount for greater than 3 s.

Action Taken When the DTC Sets

• DTCs P0234 and P0299 are Type B DTCs.
• The ECM will disable boost control and limit the system to mechanical boost only, resulting in a substantial decrease in engine power.

Conditions For Clearing the MIL/DTC

DTCs P0234 and P0299 are Type B DTCs.

Diagnostic Aids

• The charge air cooler is connected to the turbocharger and to the throttle body by flexible duct work that requires the use of special high torque fastening clamps. These clamps cannot be substituted. In order to prevent any type of air leak when servicing the ductwork, the tightening specifications and proper positioning of the clamps is critical, and must be strictly adhered to.
• Use a solution of dish soap and water in a spray bottle to pinpoint any air leaks.

Reference Information

Schematic Reference

Engine Controls Wiring Schematics (LTG)

Connector End View Reference

Component Connector End View Index

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

GE-23738-A Vacuum Pump

For equivalent regional tools, refer to Special Tools (diagnostic tools) and Special Tools (Mechanical Tools).

Circuit/System Verification

1. Ignition On.

2. Verify DTC P0106, P0107, P0108, P0236, P0237, P0238, P0243, P0245, P0246, P2227, P2228, P2229, or P2230 is not set.

• If any of the DTCs are set

Refer to Diagnostic Trouble Code (DTC) List - Vehicle.

• Go to next step: If none of the DTCs are set

3. Verify the scan tool BARO Sensor parameter is within the range specified in the Altitude Versus Barometric Pressure table for the current testing altitude.

• If not within the range.

Refer to DTC P2227-P2230.

• Go to next step: If within the range.

4. Verify the scan tool MAP Sensor and BARO Sensor parameters are within 3 kPa (0.4 psi).

• If not within 3 kPa (0.4 psi).

Refer to DTC P0106.

• Go to next step: If within 3 kPa (0.4 psi).

5. Verify the scan tool Boost Pressure Sensor and BARO Sensor parameters are within 3 kPa (0.4 psi).

• If not within 3 kPa (0.4 psi).

Refer to DTC P0236.

• Go to next step: If within 3 kPa (0.4 psi).

6. Verify a click is heard or felt from the Q40 Turbocharger Bypass Solenoid Valve when commanding the Turbocharger Bypass Solenoid Valve between Active and Inactive with a scan tool.

• If a click is not heard or felt

Refer to DTC P0033-P0035.

• Go to next step: If a click is heard or felt

7. Verify the parameters listed below do not display Malfunction when commanding the Turbocharger Bypass Solenoid Valve between Active and Inactive with a scan tool.

• Turbocharger Bypass Solenoid Valve Control Circuit High Voltage Test Status
• Turbocharger Bypass Solenoid Valve Control Circuit Open Test Status
• Turbocharger Bypass Solenoid Valve Control Circuit Low Voltage Test Status
• If Malfunction is displayed

Refer to DTC P0033-P0035.

• Go to next step: If Malfunction is not displayed

8. Verify a series of clicks, which increase in frequency, are heard or felt from the Q42 Turbocharger Wastegate Solenoid Valve when commanding the Turbocharger Wastegate Solenoid Valve between 15 - 100 % with a scan tool.

• If a series of clicks in increasing frequency are not heard or felt

Refer to DTC P0243, P0245, or P0246.

• Go to next step: If a series of clicks in increasing frequency is heard or felt

9. Verify the parameters listed below do not display Malfunction when commanding the Turbocharger Wastegate Solenoid Valve between 15 - 100 % with a scan tool.

• Turbocharger Wastegate Solenoid Valve Control Circuit High Voltage Test Status
• Turbocharger Wastegate Solenoid Valve Control Circuit Open Test Status
• Turbocharger Wastegate Solenoid Valve Control Circuit Low Voltage Test Status
• If Malfunction is displayed

Refer to DTC P0243, P0245, or P0246.

• Go to next step: If Malfunction is not displayed

10. Verify the scan tool MAP Sensor parameter and the Boost Pressure Sensor parameter are within 20 kPa (2.9 psi) during a WOT acceleration at the time of the 1-2 shift.

• If not within 20 kPa (2.9 psi)

Refer to Circuit/System Testing.

• Go to next step: If within 20 kPa (2.9 psi)

11. 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 data.

12. Verify a DTC does not set.

• If a DTC sets

Refer to Circuit/System Testing

• Go to next step: If a DTC does not set

13. All OK

Circuit/System Testing

1. Verify the conditions listed below do not exist:

• Loose clamps, cracks or other damage in the air intake duct system
• Collapsed or restricted intake duct system
• Restricted air filter
• Any air flow restriction
• Any air leak between the turbocharger and the throttle body, including the charge air cooler assembly
• Splits, kinks or improper connections at the vacuum hoses
• Any vacuum leak
• Restricted, leaking or incorrect routing of hoses going to the components listed below:
  • Q42 Turbocharger Wastegate Solenoid Valve
  • Turbocharger wastegate actuator
  • Turbocharger
• Missing, restricted or leaking exhaust components. Refer to Symptoms - Engine Exhaust.
• Exhaust leak between the turbocharger and the exhaust manifold
• Restricted or leaking turbocharger oil supply line
• Loose or incorrect installation of any components
• If a condition exists

Repair or replace the affected component as necessary.

• Go to next step: If none of the conditions exist

2. Ignition Off, disconnect the turbocharger wastegate solenoid valve supply hose at the turbocharger and apply 51 kPa (15 inches Hg) of vacuum to the hose with the GE 23738-A , ignition On.

3. Verify the pressure decreases to 0 kPa (0 inches Hg) when commanding the Turbocharger Wastegate Solenoid Valve to 15 % with a scan tool.

• The pressure does not decrease to 0 kPa (0 inches Hg)

Replace the Q42 Turbocharger Wastegate Solenoid Valve

• Go to next step: The pressure decreases to 0 kPa (0 inches Hg)

4. Connect the turbocharger wastegate solenoid valve supply hose to the turbocharger.

5. Disconnect the hose from the turbocharger wastegate actuator and connect the exhaust/pressure port of the GE 23738-A , or a suitable hand pressure pump, to the actuator.

6. Verify the wastegate actuator rod moves when applying pressure to the actuator.

• If the actuator does not move

1. Disconnect the wastegate actuator arm from the wastegate.
2. Verify the wastegate actuator rod moves when applying pressure to the actuator.
   • If the actuator does not move, replace the turbocharger wastegate actuator.
   • If the actuator moves, replace the turbocharger.

• Go to next step: If the actuator moves

NOTE: Leave harness connector connected or re-connect it after removing valve.

7. Ignition Off, remove the Q40 Turbocharger Bypass Solenoid Valve from the turbocharger, ignition On.

8. Verify the Q40 Turbocharger Bypass Solenoid Valve plunger retracts and extends when commanding the Turbocharger Bypass Solenoid Valve between Active and Inactive with a scan tool.

• The valve plunger does not retract and extend

Replace the Q40 Turbocharger Bypass Solenoid Valve

• Go to next step: The valve plunger retracts and extends

9. Verify the conditions listed below do not exist with the turbocharger assembly. Refer to Camshaft Cover and Compressor Air Intake Turbocharger Cleaning and Inspection

• Cracked, damaged or worn turbine blades
• Restricted wastegate, turbine, ports or passages
• Foreign material
• A condition exists

Repair or replace the turbocharger as necessary

• Go to next step: None of the conditions exist

10. Replace the turbocharger.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

• Turbocharger Replacement
• Turbocharger Bypass Valve Solenoid Replacement
• Turbocharger Wastegate Actuator Replacement
• Turbocharger Wastegate Regulator Solenoid Valve Replacement
• Control Module References for ECM replacement, programming, and setup

READ NEXT: