P04A8Exhaust Pressure Control Valve B Position Sensor/Switch Circuit 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. P04A8 means valve B's position signal is below its window. Bentley's Continental and Flying Spur V8 of 2023 report it for bank 2 together with P04A0 as a sensor short to ground, often stored as sporadic; wiring and contacts are checked, otherwise the actuator is replaced and the basic setting carried out.
- What you may notice
- Check engine light on
- Flap without function, exhaust sound changed
- VW/Audi TDI: EGR fault P0401 possible
- Likely causes
- LikelySignal wire shorted to ground (chafed at the underbody)
- LikelyPosition sensor or actuator faulty internally
- Possible5 V sensor supply open or shorted
- PossibleMoisture or corrosion in the connector
- 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 – €900
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.