For 1990-2009 cars

### 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: Turbocharger Engine Overboost
DTC P0299: Turbocharger Engine Underboost

### Diagnostic Fault Information

Circuit | Short to Ground | High Resistance | Open | Short to Voltage | Signal Performance
--- | --- | --- | --- | --- | ---
5-Volt Reference | P0107, P0193, P0236, P0642 | P0236, P0237 | P0107, P0236 | P0036, P0193, P0236, P050A, P0606, P0643 | P0236
Boost Pressure Sensor Signal | P0237 | P0236, P0237 | P0238 | P0238 | P0234, P0236, P0299
Low Reference | -- | P0234, P0236, P0238 | P0098, P0099, P0238 | -- | --

### Typical Scan Tool Data

#### Boost Pressure Sensor

Circuit | Short to Ground | Open | Short to Voltage
--- | --- | --- | ---
Parameter Normal Range: BARO to 240 kPa Operating Conditions: Engine running
5-Volt Reference | 20-80 kPa | 30-80 kPa | 20-80 kPa
Boost Pressure Sensor Signal | 0 kPa | 276 kPa | 276 kPa
Low Reference | -- | 276 kPa | --

### Circuit Description

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, intake air temperature (IAT), barometric pressure (BARO), and the efficiency of the charge air cooler (CAC). A diaphragm within the sensor is displaced by the pressure changes that occur from the varying load and operating conditions of the engine. The sensor translates this action into electrical resistance. The boost pressure sensor has the following circuits:

• | A shared and regulated 5-volt reference circuit

• | A shared low reference circuit

• | A boost pressure sensor signal circuit

• | The IAT sensor 2 signal circuit

The sensor provides a signal voltage to the engine control module (ECM), relative to the pressure changes, on the boost pressure sensor signal circuit. The ECM converts the signal voltage input to a pressure value.

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. The least pressure that occurs is when the vehicle is idling or decelerating, and it is equal to the BARO. The ECM monitors the boost pressure sensor signal for performance and for pressure outside of the normal range.

### Conditions for Running the DTC

#### P0234

• | DTCs P0236, P0237, P0238 are not set.

• | The driver requested boost pressure level exceeds the level of the base boost pressure.

• | This DTC runs continuously within the enabling conditions.

#### P0299

• | DTCs P0236, P0237, P0238, P0243, P0245, P0246, P2227, P2228, P2229, are not set.

• | The BARO is greater than 65 kPa.

• | The engine speed is between 3,000-6,300 RPM.

• | The ECM is not in limp home mode.

• | The ECM is not in limp home mode with safety fuel cut-off activated.

• | The driver requested boost pressure level exceeds the level of the base boost pressure.

• | This DTC runs continuously within the enabling conditions.

### Conditions for Setting the DTC

#### P0234

The ECM detects that the actual boost pressure is greater than the desired boost pressure for greater than 3 seconds continuously or 50 seconds cumulative.

#### P0299

The ECM detects that the actual boost pressure is less than the desired boost pressure for greater than 4 seconds continuously or 50 seconds cumulative.

### Action Taken When the DTC Sets

DTCs P0234 and P0299 are Type B DTCs.

### Conditions for Clearing the MIL/DTC

DTCs P0234 and P0299 are Type B DTCs.

### Diagnostic Aids

Important: The boost pressure sensor signal circuit is pulled high in the ECM with the sensor disconnected.

At ignition ON, a normal voltage measurement of the signal circuit with a DMM is 5.60 volts.

• | A restriction in the boost pressure sensor port will cause the sensor to be sluggish or unresponsive.

• | Verify that the sensor is properly installed and tightened to the proper specification.

• | The CAC 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.

• | A restriction that exists in the exhaust system will hinder the performance of the engine and the turbocharger. Refer to Restricted Exhaust .

### Reference Information

#### Schematic Reference

Engine Controls Schematics

#### Connector End View Reference

• | Engine Control Module Connector End Views

• | Engine Controls Connector End Views

#### Description and Operation

• | Turbocharger System Description

• | Boost Control 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

• | Scan Tool Data List

• | Scan Tool Data Definitions

• | Scan Tool Output Controls

• | Scan Tool Snapshot Procedure

### Circuit/System Verification

Important: Verify that the engine is in good mechanical condition before continuing with this diagnostic.

• | Verify the integrity of the entire air induction system by inspecting for the following conditions:

- | Any damaged components, including the turbocharger, the CAC, and the turbo charger wastegate actuator solenoid valve

- | Any hairline fractures of the boost pressure sensor housing

- | Loose or improper installation

- | An air flow restriction

- | Any vacuum leak

- | Any pin holes or breaks in the 3 vacuum hoses attached to the TC wastegate actuator solenoid valve

- | Any restrictions in the 3 vacuum hoses attached to the TC wastegate actuator solenoid valve

- | Any type of air leak between the turbocharger and the throttle body, including the charge air cooler (CAC) assembly.

- | In cold climates, inspect for any snow or ice buildup

• | Improper routing or connecting of the vacuum hoses on the charge air bypass valve solenoid and the turbocharger wastegate actuator solenoid valve

• | If DTC P0299 is set, then verify the proper operation of the charge air bypass valve. A stuck open valve will cause a lack of power and an underboost condition. Refer to Turbocharger Cleaning and Inspection .

• | Use the scan tool output controls to command the TC Bypass Solenoid ON and OFF. An audible click should be heard and felt.

• | Use the scan tool output controls to command the TC Wastegate Solenoid ON and OFF. An audible series of clicks should be heard and felt between 20-90 percent.

• | Determine the current vehicle testing altitude. Ignition ON, observe the scan tool MAP Sensor parameter, the Boost Pressure Sensor parameter, and the BARO Sensor parameter. Compare the parameters to each other and to the Altitude versus Barometric Pressure Table. Refer to Altitude Versus Barometric Pressure .

• | Engine idling, observe the scan tool and compare the Boost Pressure Sensor parameter to the BARO Sensor parameter. They should be within 4 kPa of each other.

### Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the boost pressure sensor.
2. Ignition OFF for 90 seconds, test for less than 5 ohms of resistance between the low reference circuit terminal A and ground.

⇒ | If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the ECM.

3. Ignition ON, test for 4.8-5.2 volts between the 5-volt reference circuit terminal C and ground.

⇒ | If less than the specified range, test the 5-volt reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the ECM.

⇒ | If greater than the specified range, test the 5-volt reference circuit for a short to voltage. If the circuit tests normal, replace the ECM.

4. Verify the scan tool Boost Pressure Sensor parameter is greater than 275 kPa.

⇒ | If less than the specified range, test the signal circuit terminal D for a short to ground. If the circuit tests normal, replace the ECM.

5. Install a 3A fused jumper wire between the signal circuit terminal D and the low reference circuit terminal A. Verify the scan tool Boost Pressure Sensor parameter is less than 1 kPa.

⇒ | If greater than the specified range, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the ECM.

6. If the circuits test normal, replace the boost pressure sensor.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Intake Air Pressure and Temperature Sensor Replacement

• | Turbocharger Wastegate Actuator Replacement

• | Control Module References for ECM replacement, setup, and programming