What does code P0478 mean?

Q: What does code P0478 mean?

Exhaust Pressure Control Valve High. P0478 means the powertrain control module (PCM) has detected that the exhaust pressure control valve circuit is reporting a voltage or position that is higher than the commanded value, indicating the valve is stuck open, stuck closed, or the feedback signal is out of range. The PCM compares the commanded valve position to the actual position from the valve position sensor and sets this code when the actual reading exceeds the expected high threshold for a calibrated time.

DTC codes / P04xx · Auxiliary emission controls / P0478

P0478Exhaust Pressure Control Valve High

P0478 means the powertrain control module (PCM) has detected that the exhaust pressure control valve circuit is reporting a voltage or position that is higher than the commanded value, indicating the valve is stuck open, stuck closed, or the feedback signal is out of range. The PCM compares the commanded valve position to the actual position from the valve position sensor and sets this code when the actual reading exceeds the expected high threshold for a calibrated time.

SystemPowertrain

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaAuxiliary emission controls

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.