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 RPM and 3,600 RPM. |
Conditions for Setting the DTC
The measured boost pressure is above the expected range by 35 kPa or 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 - Engine Controls? | -- | Go to Step 2 | |
2 |
Is DTC P0045, P0046, P0653, P2229, P2563, P2564 or P2565 also set? | -- | Go to Step 2 | |
3 |
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 4 | Go to Step 6 |
4 |
Is the voltage more than the specified value? | 0.2 V | Go to Step 5 | Go to Step 7 |
5 | Test the boost sensor low reference circuit for an open and for high resistance. Refer to Testing for Continuity and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 8 |
6 | Remove and inspect the turbocharger for wear or damage. Refer to Turbocharger Replacement and Turbocharger Cleaning and Inspection in Engine Mechanical. Did you find a condition with the turbocharger? | -- | Go to Step 9 | Go to Diagnostic Aids |
7 | 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 in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 10 |
8 | 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 in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 11 |
9 | Replace the turbocharger. Refer to Turbocharger Replacement in Engine Mechanical. Did you complete the replacement? | -- | Go to Step 12 | -- |
10 | Replace the boost sensor. Refer to Turbocharger Pressure Sensor Replacement . Did you complete the replacement? | -- | Go to Step 12 | -- |
11 | Replace the ECM. Refer to Engine Control Module Replacement . Did you complete the replacement? | -- | Go to Step 12 | -- |
12 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 13 |
13 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK | |
