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 pressure, 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 diagnosis of the BARO sensor. The highest manifold pressures occur when the turbocharger output is high. Manifold pressure can range from 58 kPa (8 psi) when pressures are low to more than 240 kPa (34 psi) when pressures are high, depending on the BARO. The boost pressure sensor has a range of 33 kPa (4 psi) to 255 kPa (36 psi). The ECM also uses the boost pressure sensor to provide engine overboost protection. The ECM calculates a predicted value for the boost pressure sensor. The ECM then compares the predicted value to the sensor input. If the ECM detects that the boost pressure sensor input is above the predicted range, this DTC will set.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P0234 Turbocharger Engine Overboost

Conditions for Running the DTC

    • DTC P0238 is not set.
    • The engine speed is between 500-3,600 RPM.
    • DTC P0234 runs continuously once the above conditions are met.

Conditions for Setting the DTC

The measured boost pressure is above the expected range by 35 kPa for more for 12 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.

Diagnostic Aids

    • Any changes to the induction system or exhaust system, such as the installation of aftermarket parts, may cause this DTC to set.
    • If the condition is intermittent, refer to Intermittent Conditions .

Step

Action

Values

Yes

No

Schematic Reference: Altitude Versus Barometric Pressure

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

1

Did you perform the Diagnostic System Check - Vehicle?

--

Go to Step 2

Go to Diagnostic System Check - Vehicle

2

  1. Turn ON the ignition, with the engine OFF.
  2. Monitor the DTC information with a scan tool.

Is DTC P0045, P0046, P2563, P2564 or P2565 also set?

--

Go to Diagnostic Trouble Code (DTC) List - Vehicle

Go to Step 3

3

  1. Install a scan tool.
  2. Start the engine.
  3. Monitor the DTC information with the scan tool.

Does the scan tool indicate that DTC P2229 is current?

--

Go to DTC P2229

Go to Step 4

4

  1. Allow the engine to reach operating temperature.
  2. Turn OFF the ignition for 30 seconds.
  3. Turn ON the ignition, with the engine OFF.

Does the scan tool indicate that the difference between the boost sensor pressure and the barometric pressure (BARO) sensor pressure is more than the specified value?

10 kPa

Go to Step 5

Go to Step 7

5

  1. Turn OFF the ignition.
  2. Disconnect the boost sensor harness connector.
  3. Connect a jumper wire between each of the terminals in the boost sensor harness connector and the corresponding terminal at the boost sensor. Refer to Using Connector Test Adapters .
  4. Turn ON the ignition, with the engine OFF.
  5. Measure the voltage from the low reference circuit of the boost sensor at the jumper wire terminal to a good ground with a DMM. Refer to Measuring Voltage Drop .

Is the voltage more than the specified value?

0.2 V

Go to Step 6

Go to Step 8

6

Test the boost sensor low reference circuit for an open and for high resistance. Refer to Testing for Continuity and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 13

Go to Step 9

7

Remove and inspect the turbocharger for wear or damage. Refer to Turbocharger Replacement and Turbocharger Cleaning and Inspection .

Did you find a condition with the turbocharger?

--

Go to Step 10

Go to Diagnostic Aids

8

Test for an intermittent and for a poor connection at the boost sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

--

Go to Step 13

Go to Step 11

9

Test for an intermittent and for poor connection at the engine control module (ECM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

--

Go to Step 13

Go to Step 12

10

Replace the turbocharger. Refer to Turbocharger Replacement .

Did you complete the replacement?

--

Go to Step 13

--

11

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

Did you complete the replacement?

--

Go to Step 13

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12

Replace the ECM. Refer to Control Module References for replacement, setup, and programming.

Did you complete the replacement?

--

Go to Step 13

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13

  1. Clear the DTCs with a scan tool.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Perform the turbocharger learn procedure. Refer to Turbocharger Learn .
  5. 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 14

14

Observe the Capture Info with a scan tool.

Are there any DTCs that have not been diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List - Vehicle

System OK