Meaning
The pressure sensor after the turbo reads pressure above the upper limit. The computer limits power to protect the engine.
Urgency
High. Overpressure stresses the engine and turbo. The car usually goes into emergency mode.
It affects
Turbo diesels and turbo gasoline engines. Wastegate or variable geometry, control, sensor.
What does P0234 mean
The pressure of the turbo is limited by a valve (wastegate), which diverts the gases past the turbine, or by movable vanes (variable geometry). If the valve doesn't open or the vanes are stuck in the high pressure position, the turbo "inflates" more than allowed. The opposite—underpressure—is P0299.
Symptoms
- A jerk and then a sudden loss of power
- Emergency mode, limited revs
- Whistling from the turbo
- Knocking in gasoline engines
| Can it be driven?
Only to the service station, no load. Overpressure can damage the pistons, head gasket and the turbo itself.
Common reasons
- Stuck variable geometry — soot on the blades, especially for diesels that drive mainly in the city.
- Wastegate valve blocked or broken actuator.
- Vacuum control — hose, solenoid.
- Faulty pressure sensor (P0106) — shows more than the real thing.
- Non-original chip tuning with too high set pressure.
How we diagnose it
- We compare the commanded and actual pressure during a test ride.
- We check the movement of the actuator and the vacuum.
- We test the solenoid and the pressure sensor.
- We check the geometry or wastegate of the turbo itself.