P04AEEVAP System Purge Control Valve B Performance/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
- 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. P04AE is the function check of purge valve B: flow, tank pressure or mixture react although the valve is commanded closed. It is documented on Subaru's FA24 turbo engines (Legacy/Outback 2.4, WRX, Ascent) as a known false trigger, fixed by an engine module software update – the bulletin advises checking the software before replacing the valve. Subaru publishes no thresholds.
- What you may notice
- Check engine light on
- Rough idle or starting problems after refuelling
- Often no change in driving (software false trigger)
- Likely causes
- LikelyEngine module software (Subaru FA24: known false trigger)
- PossiblePurge valve B leaking or stuck open (charcoal dust, wear)
- RarePurge lines swapped after a repair
- RareTank pressure sensor misreading
- 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: €80 – €350
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.