P04C2: Fuel Fill Door Unlock Control Circuit High

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). P04C2 concerns the unlock circuit: the voltage in the control circuit is above the expected range – typically a short to positive, or with a low-side driver an open load circuit. Mitsubishi's Outlander PHEV from 2023 checks it with the power on, not only in refuelling mode. Mitsubishi shows a 'refuelling system service required' message for these codes and gives no drive-cycle pattern.

Low severity. Can I keep driving?You can normally keep driving. If it affects the fuel level, do not trust the gauge and refuel earlier than usual.

Symptoms

Filler door does not open or lock as commanded
Refuelling system message in the instrument cluster
Possibly check engine light

Most likely causes

Control line shorted to battery voltage
Actuator load circuit open (seen as high with a low-side driver)
Relay sticking or faulty
Module faulty

What to check, in order

Start with the simplest. You can tick off each step.

Check the connector and wiring
Check the sensor's ground and make sure the signal wire is not receiving voltage from another circuit.
Use live data to compare the reading with actual conditions
Measure power, ground, and signal
Replace the sensor if the circuit is good

Good to know

Repair difficulty: medium
It affects emissions.

What each character of P04C2 means

P: Powertrain: engine and transmission
0: Generic code: same on every make
4: Emissions
C2: Specific fault in that system

Frequently asked questions

Can I keep driving with code P04C2?

You can normally keep driving. If it affects the fuel level, do not trust the gauge and refuel earlier than usual.

What causes code P04C2?

The most common causes are: control line shorted to battery voltage; actuator load circuit open (seen as high with a low-side driver); relay sticking or faulty.

Related codes

Sources

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.