P04B4Refueling Vapor Control Valve 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
- Plug-in and some full hybrids keep the fuel tank sealed while driving, separated from the charcoal canister by a valve. When the driver presses the fuel button, the system opens the valve, lets the pressure escape into the canister and only then unlocks the filler door. A switch reports whether the door is open or closed, so that the tank can be sealed again afterwards. P04B4 is the function check of the valve between tank and canister: after the open command the tank pressure must move towards canister or ambient pressure, and if the rate of change stays below a threshold the valve counts as stuck closed (Ford patent). The tank then cannot be depressurised, the door does not unlock or only after a long delay, and during refuelling vapour cannot reach the canister. No manufacturer document available to us uses this code.
- What you may notice
- Check engine light on
- Filler door does not open after pressing the button, or only after a long delay
- Nozzle clicks off early when refuelling
- Hissing or vapour when opening the cap
- Likely causes
- LikelyValve mechanically stuck (dirt, fuel in the valve, ice)
- PossibleVapour line kinked or blocked, liquid separator blocked
- RareCanister clogged (charcoal dust, liquid fuel)
- RareTank pressure sensor sluggish or wrong
- 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: €150 – €600
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.