P04A1Exhaust Pressure Control Valve B 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
- An exhaust pressure control valve is an electrically driven flap in the exhaust with a position sensor or end-position switch, usually inside the actuator. Valve B is the second such flap; Bentley's V8 assigns A to bank 1 and B to bank 2. Documented uses are the flap behind the particulate filter of VW's and Audi's 2.0 TDI, which raises back pressure for the low-pressure EGR, and the sound flaps of Audi and Bentley. P04A1 means valve B's control circuit is low, i.e. shorted to ground; Audi defines the valve A counterpart P0477 that way. No manufacturer document available to us uses this code; the description mirrors the valve A counterpart P0477 and CARB's monitoring requirement for input and output components.
- What you may notice
- Check engine light on
- Flap without function, exhaust sound changed
- VW/Audi TDI: EGR fault P0401 possible
- Likely causes
- LikelyControl wire shorted to ground
- LikelyFlap actuator shorted internally
- PossibleChafed wire at the underbody
- 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: €100 – €800
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.