P0238

DTC P0238

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

Steps 1-4:

Steps 5-7:

Steps 8-13:

Steps 14-15:

The numbers below refer to the step numbers on the diagnostic table.
4. A short to voltage on the 5-volt reference circuit will cause DTC P0653 to set.
7. 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.