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
Intake Air Pressure 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 under various operating conditions
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 intake air pressure sensor is integrated with the intake air temperature (IAT) sensor 2. The intake air 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). The intake air pressure and temperature sensor has the following circuits:

• | 5-volt reference

• | Low reference

• | Intake Air pressure signal

• | IAT sensor 2 signal

The sensor provides a signal voltage to the engine control module (ECM), relative to the pressure changes, on the intake air 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. The least pressure that occurs is when the vehicle is idling or decelerating, and it is equal to the BARO.

### Conditions for Running the DTCs

#### P0234

• | DTCs P0236, P0237, or 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, or P2229 are not set.

• | The BARO is greater than 65 kPa.

• | The engine speed is between 2,600-3,120 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.

• | 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 intake air 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.

• | 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.

### Reference Information

#### Schematic Reference

Engine Controls Schematics

#### Connector End View Reference

Component Connector End Views

#### Description and Operation

• | Boost Control System Description

• | 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

### Circuit/System Verification

1. Verify that restrictions do not exist in the exhaust system. Refer to Restricted Exhaust.
2. If DTC P0299 is set, verify the proper operation of the charge air bypass valve. Refer to Turbocharger Cleaning and Inspection.
3. Use the scan tool output controls to command the TC Bypass Solenoid ON and OFF. An audible click should be heard and felt.
4. 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.
5. 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.
6. Use the scan tool and compare the MAP Sensor parameter to the Boost Pressure Sensor parameter during a WOT acceleration at the time of the 1-2 shift. The readings should be within 20 kPa of each other.
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. Verify the integrity of the entire air induction system including all turbocharger components by inspecting for the following conditions:

• | Any damaged components, including the turbocharger, the CAC, and the TC wastegate actuator solenoid valve

• | Any hairline fractures of the boost pressure sensor housing

• | Loose or improper installation of any components

• | An air flow restriction

• | Any vacuum leak

• | Any pinholes 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

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

• | Any type of air leak between the turbocharger and the throttle body, including the CAC assembly.

• | Verify that an exhaust leak does not exist, including the mating surface area between the turbocharger and the exhaust manifold.

2. Ignition OFF, disconnect the harness connector at the intake air pressure and temperature sensor.
3. Ignition OFF for 90 seconds, test for less than 5 ohms between the low reference circuit terminal 1 or 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.

4. Ignition ON, test for 4.8-5.2 volts between the 5-volt reference circuit terminal 3 or 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.

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

⇒ | If less than the specified range, test the signal circuit terminal 4 or D for a short to ground. If the circuit tests normal, replace the ECM.

6. Install a 3A fused jumper wire between the signal circuit terminal 4 or D and the low reference circuit terminal 1 or 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.

7. If the circuits test normal, test or replace the intake air pressure and temperature 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