P04A4Exhaust Pressure Control Valve B Stuck Open
- 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. P04A4 means valve B is commanded to close but its feedback stays open. With an EGR flap too little back pressure means too little EGR, with a sound flap the exhaust stays loud. No manufacturer document available to us uses this code; the description mirrors the valve A counterpart P047F 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
- LikelyFlap or flap shaft corroded or coked (stiff)
- PossibleFlap actuator (motor or gear) faulty or too weak
- RareLinkage between actuator and flap broken or misadjusted
- RarePosition sensor reports wrongly
- 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: €200 – €1,500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.