P04C8: Fuel Fill Door Open Request Sensor/Switch Circuit

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). P04C8 is the general circuit fault of the fuel button input. No manufacturer document available to us uses this code; the description follows CARB's rules for input and output components and patents on the door actuator.

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

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

Most likely causes

Fuel button faulty
Wire or connector between button and module open or shorted
Button ground open
Module

What to check, in order

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

Check the connector and wiring
Check the continuity of the wire between the component and the control module.
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: easy
It affects emissions.

What each character of P04C8 means

P: Powertrain: engine and transmission
0: Generic code: same on every make
4: Emissions
C8: Specific fault in that system

Frequently asked questions

Can I keep driving with code P04C8?

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

What causes code P04C8?

The most common causes are: fuel button faulty; wire or connector between button and module open or shorted; button ground open.

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.