P0234 fault code: turbo boost pressure too high
Plain-language definition
Turbocharger/Supercharger A Overboost Condition
What does it mean?
On turbocharged engines, the engine computer decides how much pressure the turbo should produce for the driving conditions and monitors the actual pressure with a sensor on the intake side. The pressure is limited either by a wastegate (bypass valve), which sends part of the exhaust gas past the turbo, or, on variable-geometry turbos, by the angle of the vanes.
P0234 is stored when the measured boost pressure goes above the allowed upper limit. Because too much pressure can strain the engine and the turbo, on many cars the engine computer limits power; that's why you may notice the car suddenly losing pulling power when you accelerate hard.
This usually comes from something sticking in the system that regulates boost pressure, or from a sensor that measures incorrectly. The check engine light may come on; sometimes the loss of power goes away when the engine is restarted, then comes back when you accelerate hard again.
How serious is it?
It's a Warning-level code, but if it keeps coming back it should be taken seriously: boost pressure getting out of control means extra strain on the engine and the turbo.
Severity is a guide; if the warning light is flashing or you notice symptoms while driving, have the car checked at a workshop.
Common general causes
- The vanes of a variable-geometry turbo (VGT) sticking because of soot or wear
- The turbo's wastegate (bypass valve) failing to open or getting stuck
- A problem with the control valve (solenoid) that manages boost pressure, or with the vacuum hoses
- The boost pressure sensor giving wrong readings, or a problem in its circuit
- Less often, a poor contact in the wiring or connectors of these valves
The list shows general causes; a workshop finds the actual cause on your car with a check.
Definitions by make
Some manufacturers record the same code under their own wording:
- Toyota
- Engine Boost Condition Limit Exceeded
Related codes
How does it appear in the 2dakika report?
Turbocharger/Supercharger A Overboost Condition
If the code is read as a confirmed (stored) fault, the report shows it with the "Warning" severity; in pending or past records, codes that don't request the warning light and aren't critical appear as "Info". If the engine computer stored them, the conditions when the fault was recorded (engine temperature, rpm, speed) are shown too.
Read this code with the OBD-X1, and clear it from the app after the repair.
Clearing the code doesn't fix the fault; if the problem persists, the code comes back.