P25B4
Turbocharger/Supercharger Wastegate A Stuck Closed
Wastegate A is mechanically stuck closed. The turbo cannot bleed off exhaust at high load — boost overshoots the setpoint, risking overboost cut-off and damage to the turbo bearing. Carbon-locked flap, seized linkage or aged actuator are typical causes.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: hard
Symptoms
- Check engine light on
- Significant power loss / limp mode
- Possible blue or black smoke from exhaust
- Whistling or hissing sound from intake
Common causes
Ordered by how often each turns out to be the cause.
- Carbon-locked wastegate flapCommon
- Seized linkagePossible
- Carbon or debris buildup preventing free movementLess likely
Parts involved
- Wastegate A
- Turbocharger A
P25B4 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.