This text explains the meaning, symptoms, possible causes, and diagnostic and repair procedures for error code P0238. This code is a generic diagnostic trouble code (DTC), meaning it can apply to all vehicles equipped with a turbocharger, including brands like VW, Dodge, Mercedes, Isuzu, Chrysler, and Jeep.
Simply put, code P0238 indicates that the Powertrain Control Module (PCM) has detected an abnormally high voltage from the turbocharger boost pressure sensor at a time when the turbocharger should not be producing pressure (no boost requested).
Here is a breakdown of the key points:
- What is it? A standard error code for turbocharged vehicles.
- How does the boost pressure sensor work? It is a variable resistor powered by a 5-volt signal from the PCM.
- Low pressure = high resistance = low return voltage to the PCM (approximately 0.5 volts).
- High pressure = low resistance = higher return voltage to the PCM (approximately 4.5 volts).
- When is code P0238 triggered? When the PCM receives a voltage higher than 4 volts from the boost pressure sensor while no boost is requested.
Common symptoms of code P0238:
- The check engine light illuminates.
- The PCM enters “limp mode,” which results in:
- Significantly reduced acceleration.
- Limited boost pressure.
- Retarded ignition timing.
- The PCM ignores data from the boost pressure sensor and uses a default value.
Possible causes of code P0238:
- Problems with other sensors or the 5-volt reference circuit (Intake Air Temperature (IAT) sensor, Engine Coolant Temperature (ECT) sensor).
- Intermittent wiring issues (loose or faulty connections).
- A faulty boost pressure sensor (“A”).
- A short to voltage in the boost pressure sensor circuit.
- A faulty Powertrain Control Module (PCM).
Suggested diagnostic and repair procedures:
- Check for other error codes: If other codes are present (especially those related to IAT, ECT sensors, or the 5-volt reference), they should be resolved first.
- Consult Technical Service Bulletins (TSBs): Check if the manufacturer has released specific information or known fixes for this issue on your vehicle.
- Wiggle test the wiring: With the engine running, gently shake the wiring harness near the boost pressure sensor to see if it triggers the fault. If it does, inspect the connections carefully.
- Check the sensor supply voltage: With the sensor disconnected and the ignition on (engine off), measure the voltage at the sensor’s power connector. It should be 5 volts. If not, the problem could be with the PCM.
- Check the sensor signal voltage: Reconnect the sensor and, with the ignition on (engine off), measure the voltage at the sensor’s signal wire. It should be approximately 0.5 volts. A significantly higher voltage suggests a faulty sensor.
- Warning: Never use an incandescent test light to test the boost pressure sensor circuits, as this could damage the sensor or the PCM. Use a digital multimeter.
Importance of prompt repair:
The text emphasizes that it is important to resolve this issue quickly due to the increased risk of catalytic converter damage when the engine runs in “limp mode” for an extended period.