P0234Turbocharger/Supercharger A Overboost Condition
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- P0234 is a function code, not a sensor fault: the engine module compares target and actual boost, and actual boost stays above target although the control is already lowering it (wastegate opened, variable vanes opened). GM petrol engines set it at 20–35 kPa over target with the warning light in the first trip; GM diesels with variable vanes at 7–10 kPa, after two trips; Ford EcoBoost at about 28 kPa (4 psi) over 5 s while the wastegate is already commanded fully open. Ford diesels instead use P0234 for exhaust back pressure above 4.0–4.5 bar. The engine limits boost or enters limp mode. Typical causes are a wastegate stuck closed, sooted variable vanes or a faulty control valve; Audi traced cases on the Q7 TDI to cracked exhaust parts jamming the turbo vanes. Check the boost sensor against barometric pressure first.
- What you may notice
- Check engine light on
- Limp mode with clear loss of power
- Boost overshoots on acceleration, then power drops
- Knocking under full load (petrol) or smoke (diesel)
- Likely causes
- LikelyWastegate stuck closed, actuator or linkage sticking, control hose off or blocked
- LikelyVariable turbine vanes sooted or stuck closed (diesel)
- PossibleBoost control valve or electric actuator faulty
- PossibleBoost or manifold sensor reading too high (drift)
- RareSoftware or calibration, tuning
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Usually a job for a workshop.Typical cost: €60 – €2,500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.