P0034Turbocharger/Supercharger Bypass Valve A Control Circuit Low
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- The turbocharger bypass valve A is the compressor recirculation (diverter) valve: it connects the pressure side of the compressor with the intake side upstream of the turbocharger. It opens when the throttle closes quickly at high boost, so the compressor does not surge and the compressor wheel keeps its speed for the next acceleration. It is not the wastegate, which bypasses exhaust gas around the turbine and has its own codes. The valve is either electric or a vacuum unit controlled by a solenoid. P0034 means the voltage at the control output is too low, typically because the control wire is shorted to ground; on some control modules an open circuit also sets this code.
- What you may notice
- Check engine light on
- Fluttering or hissing when lifting off the throttle if the valve stays closed
- Weak response after gear changes
- Too little boost if the valve stays open
- Likely causes
- LikelyControl wire shorted to ground
- PossibleValve shorted internally
- PossibleSupply missing, e.g. fuse or main relay
- RareOutput driver in the engine control module faulty
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Often possible to do yourself.Typical cost: €50 – €350
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.