P0039
Turbocharger/Supercharger Bypass Valve A Control Circuit Range/Performance
The wastegate or bypass valve A on the turbo/supercharger does not respond mechanically as expected to its control signal. Boost pressure deviates from target.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: medium
Symptoms
- Charge status indicator shows fault
- Charging may not start or interrupts
- Slower-than-expected charge rate
Common causes
Ordered by how often each turns out to be the cause.
- Wastegate sticking from carbonCommon
- Vacuum/boost line leakingPossible
- Wastegate actuator wornPossible
Parts involved
- Wastegate Actuator
- Bypass Valve
- Boost Pressure Sensor
P0039 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.