P04B8Fuel Fill Door Position Sensor/Switch Circuit
- 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. P04B8 is the general circuit fault or open circuit of the door switch: the module cannot read the door state. If the door state is unknown, the system leaves the tank open to the canister as a precaution and suspends the leak tests. No manufacturer document available to us uses this code; the description follows CARB's input component rules and patents for the door switch.
- What you may notice
- Check engine light on
- Fuel door open message although the door is closed, or missing when it is open
- Door may not open or only after a delay
- EVAP readiness not set
- Likely causes
- LikelyWire or connector at the door switch open (side panel, moisture)
- PossibleSwitch or sensor faulty internally
- PossibleGround or supply interrupted
- RareModule input faulty
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Easy · Often possible to do yourself.Typical cost: €30 – €250
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.