Powertrain, generic · Auxiliary emission controls

P04B5 Fuel Fill Door Stuck Open

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

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. P04B5 means the door is not detected as closed and latched although the system expects it to be. Ford (C-Max and Fusion Energi 2013–17, MKZ hybrid) names a door not fully latched or opened by an accidental button press, with a message and the code in the third drive cycle; on the MKZ a door pressed during unlocking can confuse the latch – reset by pressing the button and waiting 12 s. Stellantis re-enables the check only after more than 16 miles and names a missing plunger or magnet, the cap tether blocking it, or a short to ground of the status line.

Likely causes

Door not fully latched after refuelling or opened by an accidental button press
Fuel cap tether blocking the plunger or latch
Plunger missing or loose, magnet or latch motor shifted or faulty
Status line of the door switch shorted to ground

Symptoms

  • Check engine light on (depending on the maker)
  • Fuel door open message in the instrument cluster
  • Door stays open or does not latch

Repair estimate

DifficultyEasyDIY possible
Parts and labour€0–250
Time0.2–1.5 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

fuel fill doorfuel fill door latchfuel fill door position switchengine control module

Related codes

P04B6P04B8P04DCP04B4P0457

References: static.nhtsa.gov, static.nhtsa.gov, static.nhtsa.gov, static.nhtsa.gov.