OBD-II code · Powertrain (generic)
P04B9 Fuel Fill Door Position Sensor Circuit Low
Same as P04B8 with the signal voltage below the plausible range. Wiring faults of this kind typically come from chafing, water ingress at connector seals, or pin push-back — a wiggle test on the harness while the code is active often confirms the location.
Is it safe to drive with P04B9?
Usually safe to drive in the short term. Get it diagnosed when convenient, sooner if the car drives differently.
Common causes
- Most likelySignal shorted to ground
- Less likelyConnector pins corroded - high contact resistance
- Less likelyHarness chafing through insulation
Repair at a glance
- Difficulty
- Easy
- DIY friendly
- Often, with basic tools
- Typical labour
- 0.4–1.2 h
- Emissions test
- Usually unaffected
- Parts involved
- Fuel Fill Door Position Sensor
Related codes
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.