P0238

What it means

P0238 means the engine control unit has seen the signal voltage from the turbocharger or supercharger boost pressure sensor 'A' circuit rise above the expected range. This usually points to a short to voltage, an open circuit in the sensor ground, or a faulty sensor, rather than a genuine overboost. The unit often limits boost and may switch to a reduced power mode.

Symptoms

• Engine warning light on
• Reduced power or limp mode
• Turbo boost feels flat or inconsistent
• Poor acceleration and hesitation under load
• Rough running or unusual fuelling, such as black smoke
• Possible stored overboost or boost-related codes alongside

Possible causes

• Faulty boost pressure sensor reading high or stucklikely
• Damaged, chafed or corroded wiring to the sensor, including a short to the supply voltage or signal wirelikely
• Poor connection or water ingress in the sensor connector, including a high-resistance or open groundlikely
• Open circuit on the sensor ground wire or reference supply faultpossible
• Blocked or damaged vacuum or pressure feed to the sensor, where fittedpossible
• Genuine overboost caused by a stuck wastegate, boost control or variable geometry faultpossible
• Internal fault in the engine control unitrare

How to diagnose

1. Read all stored and pending codes and note the freeze frame data, such as engine load, rpm and boost reading when the code set.
2. Check for other codes, especially other sensor supply voltage or boost control faults, as these can point to a shared supply fault.
3. Inspect the sensor, connector and wiring for damage, chafing, heat damage, corrosion and moisture, and check the connector pins are tight.
4. With the ignition on and engine off, view the live boost sensor reading and compare it with atmospheric pressure; a high or fixed reading suggests a sensor or wiring fault.
5. Unplug the sensor and check the supply, signal and ground circuits against the manufacturer's wiring data for shorts to voltage, open circuits and high resistance.
6. Check any vacuum or pressure hose feeding the sensor for splits, blockages or oil contamination.
7. Compare live boost with the target boost on a road test or under load to rule out a genuine overboost, and inspect wastegate or boost control operation; the method depends on the engine.
8. If wiring and supply are sound, test or swap in a known good sensor, following the manufacturer's procedure for that model.

How to fix

• Replace the boost pressure sensor if it is faulty or reading out of range.
• Repair or replace damaged wiring and fix any short to voltage or open ground circuit.
• Clean, dry or replace corroded or loose connector terminals.
• Clear or replace blocked or damaged pressure feed hoses.
• Repair the cause of any genuine overboost, such as a sticking wastegate, faulty boost control valve or variable geometry actuator.
• Clear the code after repair and road test to confirm it does not return.

Can I keep driving?

Nearby codes

• P0237GenericTurbocharger/Supercharger Boost Sensor A Circuit Low
• P0239GenericTurbocharger/Supercharger Boost Sensor B Circuit