What does it mean?
On vehicles with a powered or locking fuel filler door, a module controls the door and reads a position sensor or switch that reports whether it is open or closed. P04B5 is stored when that feedback keeps saying the door is open even though the module has commanded it closed, or after the door has clearly been shut. This is a mechanical or feedback fault rather than a simple circuit fault: the module has a command and a position report that do not agree, and the report is stuck at the open state. On sealed tank systems the module needs to know the door is properly closed before it can seal and pressurise the fuel system, so this code often blocks evaporative monitors as well. It also matters for security, because the fuel filler cannot be locked while it is reported open.
Symptoms
- Fuel filler door will not stay closed or pops back open
- Warning message about the fuel filler door on vehicles that display one
- MIL (check engine lamp) on with evaporative monitors that will not run
- Fuel filler cannot be locked with the vehicle
- Live data still shows the door as open with the door physically closed
- Wind noise or a rattle from the filler door area while driving
Likely causes
- Door hinge, latch or striker bent or damaged after a minor impact or forced opening
- Ice, dirt or debris in the latch area preventing the door from seating fully
- Broken or detached return spring in the filler door mechanism
- Position switch stuck in the open state by corrosion or a jammed plunger
- Misaligned door panel so the switch never sees the closed position even when the door looks shut
- Actuator motor or solenoid that has failed with the mechanism in the open position
- Damaged wiring or a shorted position circuit that reports the open state permanently
How to fix it
- Open and close the door by hand and watch the position status in live data to see whether the report ever changes
- Inspect the door, hinge, latch and striker for bending, damage, ice, dirt or a broken spring
- Check panel alignment and the gap around the door, since a small misalignment can keep the switch from being triggered
- Actuate the switch plunger directly by hand while watching live data to separate a mechanical problem from an electrical one
- Measure the switch circuit at the connector, checking for a permanent short or a stuck contact
- Repair or realign the mechanism, or replace the switch or the actuator according to the results
- Clear the code, cycle the door several times and confirm the status follows the door reliably