Powertrain, generic · Auxiliary emission controls

P04CB Fuel Fill Door Open Request Sensor/Switch Circuit High

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

On plug-in hybrids with a sealed, pressurised tank, pressing the fuel button (open request) starts a refuelling mode: the module opens the tank valve, releases the pressure into the charcoal canister and only then unlocks the filler door via an electric actuator (Ford patent). P04CB means the button line is above its valid range. On Mitsubishi's Outlander PHEV from 2023 the engine module feeds the button and a press pulls the line to ground; P04CB sets if the line carries battery voltage for 2 s, i.e. a short to positive. Mitsubishi shows a 'refuelling system service required' message for these codes and gives no drive-cycle pattern.

Likely causes

Button line shorted to positive
Fuel button faulty
Connector or wiring damaged
Module

Symptoms

  • Fuel button has no effect, door does not open
  • Refuelling system message in the instrument cluster
  • Refuelling only via emergency release

Repair estimate

DifficultyEasyDIY possible
Parts and labour€20–200
Time0.3–1.5 h

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

Parts involved

fuel door open request switchswitch wiringengine control module

Related codes

P04C8P04C9P04CAP04CCP04CDP04BF

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