P04BD: Fuel Fill Door Lock Control Circuit Low

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). P04BD concerns the lock circuit: the voltage in the control circuit is below the expected range – typically the control line is shorted to ground. A separate lock output exists only on actuators that drive actively in both directions; spring-return actuators have only the unlock circuit. 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

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 chafed against the body (short to ground)
Water or corrosion at the connector
Actuator shorted internally
Relay or module driver faulty

What to check, in order

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

Check the connector and wiring
With the connector unplugged, check whether the signal wire is making contact with ground.
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 P04BD means

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

Frequently asked questions

Can I keep driving with code P04BD?

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

What causes code P04BD?

The most common causes are: control line chafed against the body (short to ground); water or corrosion at the connector; actuator shorted internally.

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.