Powertrain, generic · Auxiliary emission controls

P04B7 Fuel Fill Door Position Sensor/Switch Circuit Intermittent/Erratic

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. P04B7 means the door switch signal drops out or jumps briefly – the state changes without the door moving, for example while driving. Typical are loose contacts or a broken wire at the bend into the door area. 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.

Likely causes

Loose contact in the connector, pins pushed back
Broken wire at the bend or grommet
Switch bouncing or worn, door seated loosely
Module input faulty

Symptoms

  • 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

Repair estimate

DifficultyEasyDIY possible
Parts and labour€30–250
Time0.5–1.5 h

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

Parts involved

fuel fill door position switchswitch wiringengine control module

Related codes

P04B8P04B9P04BAP04DCP04B5

References: law.cornell.edu, patents.google.com, patents.google.com.