GM Service Manual Online
For 1990-2009 cars only

Circuit Description

The boost pressure sensor measures the pressure inside the intake manifold. Pressure in the intake manifold is affected by turbocharger output, engine speed, accelerator pedal input, air temperature, and barometric pressure (BARO). A diaphragm within the boost pressure 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 wiring includes 3 circuits. The engine control module (ECM) supplies a regulated 5 volts to the sensor on a 5-volt reference circuit. The ECM supplies a ground on a low reference circuit. The boost pressure sensor provides a signal voltage to the 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 lowest pressure that can exist in the intake manifold is equal to the BARO. This occurs when the vehicle is operated at idle or when the ignition is ON while the engine is OFF. Under these conditions, the ECM uses the boost pressure sensor to aid in the diagnosis of the BARO sensor. The highest manifold pressure occur when the turbo charger output is high. Manifold pressure can range from 58 kPa (8 psi) when pressure are low, to more than 240 kPa (34 psi) when pressure are high, depending on the BARO. The boost pressure sensor has a range of 33-255 kPa (4-36 psi). The ECM also uses the boost pressure sensor to provide engine overboost protection.

The ECM monitors the boost pressure sensor signal for pressure outside of the normal range. If the ECM detects a boost pressure that is excessively high, DTC P0238 sets.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P0238 Turbo Charger Boost Sensor Circuit High Voltage

Conditions for Running the DTC

The engine is running.

Conditions for Setting the DTC

The ECM detects that the boost pressure is more than 254 kPa (36 psi) for 2 seconds.

Action Taken When the DTC Sets

    • The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
    • The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

Conditions for Clearing the MIL/DTC

    • The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
    • A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
    • A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
    • Clear the MIL and the DTC with a scan tool.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. A short to voltage on the 5-volt reference circuit will cause DTC P0653 to set.

  2. This step tests the signal circuit of the boost pressure sensor for a short to voltage. The short may backfeed through the sensor to the 5-volt reference circuit causing DTC P0653 to set.

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

Connector End View Reference: Engine Control Module Connector End Views or Engine Controls Connector End Views

1

Did you perform the Diagnostic System Check - Engine Controls?

--

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2

  1. Turn ON the ignition, with the engine OFF.
  2. Observe the Boost Pressure Sensor parameter with a scan tool.

Is the pressure more than the specified value?

254 kPa (36 psi)

Go to Step 4

Go to Step 3

3

  1. Observe the Freeze Frame/Failure Records for this DTC.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. 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.

Did the DTC fail this ignition?

--

Go to Step 4

Go to Intermittent Conditions

4

Monitor the Diagnostic Trouble Code (DTC) Information with a scan tool.

Does the scan tool indicate that DTC P0653 is also set?

--

Go to Step 7

Go to Step 5

5

  1. Turn OFF the ignition.
  2. Disconnect the electrical connector of the boost pressure. Refer to Turbocharger Pressure Sensor Replacement .
  3. Turn ON the ignition, with the engine OFF.

Does the scan tool indicate that the Boost Pressure Sensor parameter is less than the specified value?

36 kPa (5 psi)

Go to Step 6

Go to Step 8

6

  1. Remove the boost pressure sensor.
  2. Connect a jumper wire between each of the terminals in the boost pressure sensor harness connector and the corresponding terminal at the boost pressure sensor. Refer to Using Connector Test Adapters in Wiring Systems.
  3. Measure the voltage from the low reference circuit of the boost pressure sensor at the jumper wire terminal to a good ground with a DMM. Refer to Measuring Voltage Drop in Wiring Systems.

Is the voltage more than the specified value?

0.2 V

Go to Step 9

Go to Step 10

7

  1. Turn OFF the ignition.
  2. Disconnect the electrical connector of the boost pressure sensor. Refer to Turbocharger Pressure Sensor Replacement .
  3. Turn ON the ignition, with the engine OFF.

Does the scan tool indicate that the Boost Pressure Sensor parameter is less than the specified value?

36 kPa (5 psi)

Go to DTC P0653

Go to Step 8

8

Test the signal circuit of the boost pressure sensor for a short to voltage. Refer to Testing for a Short to Voltage and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 14

Go to Step 13

9

Test the low reference circuit of the boost pressure sensor for high resistance or an open. Refer to Circuit Testing in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 14

Go to Step 11

10

Inspect for poor connections at the boost pressure sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 14

Go to Step 12

11

Inspect for poor connections at the engine control module (ECM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 14

Go to Step 13

12

Replace the boost pressure sensor. Refer to Turbocharger Pressure Sensor Replacement .

Did you complete the replacement?

--

Go to Step 14

--

13

Replace the ECM. Refer to Engine Control Module Replacement .

Did you complete the replacement?

--

Go to Step 14

--

14

  1. Clear the DTCs with a scan tool.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. 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.

Did the DTC fail this ignition?

--

Go to Step 2

Go to Step 15

15

Observe the Capture Info with a scan tool.

Are there any DTCs that have not been diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List

System OK