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 P0236: Turbocharger Boost System Performance
DTC P0237: Turbocharger Boost Sensor Circuit Low Voltage
DTC P0238: Turbocharger Boost Sensor Circuit High Voltage

### 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 | P0234, P0236, P0299
Intake Air Pressure Signal | P0237 | P0236, P0237 | P0238 | P0238 | P0236
Low Reference | -- | P0234, P0236, P0238 | P0098, P0099, P0238 | -- | --

### Typical Scan Tool Data

#### Boost Pressure Sensor

Circuit | Short to Ground | Open | Short to Voltage
--- | --- | --- | ---
Operating Conditions: Engine running at various operating conditions Parameter Normal Range: BARO to 240 kPa
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 DTC

#### P0236 - Engine Cranking

• | DTCs P0107, P0108, P0121, P0122, P0123, P0221, P0222, P0223, P0237, P0238, P2227, P2228, or P2229 are not set.

• | The engine OFF timer is greater than 4 seconds.

• | The engine is cranking at less than 400 RPM for at least 200 ms.

• | This DTC runs during engine cranking only.

#### P0236 - Engine Idling

• | DTCs P0121, P0122, P0123, P0221, P0222, P0223, P0237, P0238, P2227, P2228, or P2229 are not set.

• | The engine is running and the ECM has counted greater than three revolutions.

• | The engine speed is less than 1000 RPM.

• | The TP Sensor parameter is less than 24 percent.

• | The ECM is not in limp home mode.

• | This DTC runs continuously within the enabling conditions.

#### P0237

• | The ignition is ON or the engine is running.

• | This DTC runs continuously within the enabling conditions.

#### P0238

• | The ignition is ON or the engine is running.

• | This DTC runs continuously within the enabling conditions.

### Conditions for Setting the DTC

#### P0236 - Engine Cranking

The ECM detects when the engine is cranking that the boost pressure sensor signal plus a calibrated threshold is not within range of a model derived from the BARO sensor, the MAP sensor, and the boost pressure sensor for more than 2 seconds.

#### P0236 - Engine Idling

• | The ECM detects when the engine is idling that the boost pressure sensor signal is less than 50 kPa for greater than 4 seconds continuously, or 50 seconds cumulative.

| OR

• | The ECM detects when the engine is idling that the boost pressure sensor signal plus a calibrated threshold is not within range of the BARO sensor for greater than 4 seconds continuously, or 50 seconds cumulative.

#### P0237

The ECM detects that the boost pressure sensor voltage is less than 0.19 volt for more than 4 seconds continuously, or 50 seconds cumulative.

#### P0238

The ECM detects that the boost pressure sensor voltage is greater than 4.85V for more than 4 seconds continuously, or 50 seconds cumulative.

### Action Taken When the DTC Sets

• | DTCs P0236, P0237, P0238 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 P0236, P0237, P0238 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 5.60V.

• | 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.

• | The BARO sensor is integrated within the ECM, and it has a port on the housing that allows it to sense the ambient pressure. Any restriction at this opening may hinder the operation of the BARO sensor.

### 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 DTC P0641, P0642, or P0643 is not set.

⇒ | If any of the DTCs are set, refer to DTC P0641-P0643, P0651-P0653, or P0697-P0699.

2. Ignition OFF for 90 seconds. 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.
3. 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.
4. 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.
5. 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

• | Hairline fractures of the boost pressure sensor housing

• | Hairline fractures of the MAP sensor housing

• | A buildup of contamination, snow or ice at the BARO port on the ECM

• | Loose or improper installation

• | An air flow restriction

• | Any vacuum leak

• | 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 5Ω 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 K20 ECM.

4. Ignition ON, test for 4.8-5.2V 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 K20 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 K20 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 K20 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 K20 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

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