P04AFEVAP System Purge Control Valve B Stuck Closed
- 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
- The evaporative emission (EVAP) system stores fuel vapour from the tank in a charcoal canister; a purge valve lets the engine draw it off, and a vent valve opens the canister to fresh air. Purge valve B is a second electric purge valve, usually for the high-load purge line of a turbo engine, which purges to the compressor inlet when there is boost in the manifold (Ford patent). Many makers solve this path with one purge valve and passive check valves instead – Ford tests it as P04F0 – and then have no valve B. CARB requires every purge path to be checked. P04AF is the flow check of the high-load path: under boost the module opens purge valve B, and if tank pressure or mixture do not react, the valve is stuck closed or the path is blocked – a FCA patent describes such a stepwise test. The canister is then not purged under boost and can saturate on load-heavy driving. No manufacturer document available to us uses this code; the description follows CARB and the comparable purge valve A checks (for GM P0443/P0458/P0459).
- What you may notice
- Check engine light on
- Fuel smell
- EVAP readiness not set
- Likely causes
- LikelyPurge valve B stuck closed (gummed, dirt)
- PossibleLine to the compressor inlet off, kinked or blocked, check valve sticking
- RareEngine module software or false trigger
- RareCanister or vent blocked
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Often possible to do yourself.Typical cost: €60 – €300
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.