P0234: Turbo/supercharger overboost condition
The turbo is producing more boost than the engine computer allows. Most engines cut power to protect themselves.
Updated
What P0234 means
The engine computer controls the turbo’s boost pressure: with a wastegate that lets exhaust bypass the turbo, or, on most modern diesels, with movable vanes in the turbo. A boost pressure sensor reports the result.
When the measured boost goes above the limit, the computer stores P0234 and usually cuts the power, so the engine and the turbo aren’t overloaded.
Read My Car’s live data shows the intake manifold pressure and the barometric pressure, if your car reports them. The difference between the two is the boost.
Can I keep driving?
Drive gently
Drive gently and have it checked soon. Too much boost can damage the engine and the turbo, and the engine may cut power suddenly. Avoid full throttle and overtaking until it’s fixed.
General guidance based on the code alone, not on the car’s actual condition. If in doubt, stop and ask a mechanic.
The power cut can come suddenly when you accelerate. Allow for it when overtaking or joining fast traffic.
Symptoms
- A sudden loss of power when accelerating, or limp mode.
- Surging power on some cars.
- The check engine light, sometimes only after hard acceleration.
Common causes
- Sticking wastegate or turbo vanes. Soot can make a diesel turbo’s vanes stick; a wastegate can seize.
- Faulty boost control valve, or a split or loose vacuum hose to it. On many engines the boost is controlled with vacuum, so a leaking hose upsets it.
- Faulty boost pressure sensor. A sensor that reads too high makes normal boost look excessive.
Typical fixes
- Check the vacuum hoses to the boost control for splits and loose ends.
- Have the boost control valve, and the turbo’s vanes or wastegate, checked for free movement.
- Have the boost pressure sensor checked, for example by comparing its reading with the barometric pressure with the engine off.
- Clear the code after the repair and check the power on a test drive.
Questions
Can I drive with P0234?
Gently, and have it checked soon. Too much boost can damage the engine and the turbo, and the engine may cut power suddenly. Avoid full throttle and overtaking until it’s fixed.
Is P0234 the opposite of P0299?
Yes. P0234 means too much boost, P0299 too little. The turbo’s control is involved in both, but the causes differ.