P0234: Turbocharger/Supercharger "A" Overboost Condition
The boost pressure is higher than the engine control unit allows.
High risk
Drive gently and have it checked soon: overboost can damage the engine and turbo.
Short answer · Can I keep driving with P0234?
Only gently and for short distances. The engine usually limits power. Avoid full throttle until the boost control has been checked, as too much boost can damage the engine.
What does P0234 mean?
Code P0234 means the measured boost pressure exceeded the maximum allowed value. The turbo is producing more pressure than requested, usually because the wastegate or variable vanes are not regulating it.
A stuck wastegate or variable vanes, damaged control hoses or a faulty boost pressure sensor are common causes.
What the car does when the code is set
The check engine light comes on and the engine control unit limits power (limp mode). The car still drives but accelerates slowly. The limitation is usually lifted when the engine is restarted, until the fault appears again.
How the system works
A turbocharger uses exhaust gas to drive a compressor that pushes more air into the engine. The amount of boost is controlled either by a wastegate, which lets exhaust bypass the turbine, or by variable vanes that change how the exhaust strikes it. The engine control unit sets a target boost pressure and moves the actuator to reach it, measuring the result with a boost pressure sensor. If the measured pressure exceeds the maximum allowed, it stores an overboost code and limits power to protect the engine.
Common symptoms
Possible causes
Listed without ranking. The cause on your car depends on make, engine and mileage — see the maker notes below.
- Stuck wastegate or variable vanesThe turbo cannot reduce boost.
- Faulty boost control solenoidThe solenoid does not regulate the vacuum or pressure to the actuator.
- Damaged control hosesA split or swapped vacuum hose on the boost control.
- Faulty boost pressure sensorThe sensor reads higher than the real pressure.
How it is diagnosed
- Check the hosesInspect vacuum and pressure hoses of the boost control for splits and correct routing.
- Test the actuatorCheck that the wastegate or vane actuator moves freely across its whole range.
- Compare boost readingsCompare desired and actual boost with live data, and the sensor reading with the outside air pressure with the engine off.
- Test the control solenoidCheck resistance and operation as described in the service data.
Questions about P0234
Why does the car go into limp mode?
To protect the engine from too much boost, the control unit limits power until the fault is fixed.
Can a chip tune cause overboost codes?
Yes. Modified software or boost controllers can exceed the sensor's or engine's limits and set this code.
Is this a turbo failure?
Usually not. The turbo itself works but is not being controlled correctly.