Powertrain, generic · Auxiliary emission controls

P04BA Fuel Fill Door Position Sensor/Switch Circuit High

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. P04BA means the door switch signal is above its valid range – typically an open signal or ground line pulled up by the module, or a short to positive. 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

Signal or ground line open (pull-up drives it high)
Signal line shorted to positive
Switch faulty (high resistance)
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

P04B8P04B9P04B7P04DCP04B5

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