Signal wire shorted to earth or chafed against bodywork near the filler door or rear wheel arch; Faulty position switch or sensor built into the filler door lock actuator; Corroded, wet or damaged connector at the lock actuator or in-line connectors; Seized or damaged lock actuator or mechanism causing an out-of-range reading; Open circuit in the supply or reference feed, pulling the signal low; Fault in the controlling module or its internal driver.

P04C5

Fuel Fill Door Lock Position Sensor/Switch Circuit Low.

Generic
Powertrain
Generic code
Low severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
4: AreaAuxiliary emission controls
C5: FaultThe specific fault in that area

What it means

P04C5 means the control unit has seen a voltage that is too low on the circuit for the fuel filler door lock position sensor or switch. The unit expects the signal to change between set limits as the lock moves, and it has found it stuck low, which points to a short to earth, a wiring fault or a faulty switch. Where this system is fitted and how it is wired depends on the model.

Symptoms

Warning light (MIL) on or a fuel system or lock warning shown on the dash
Fuel filler door will not open, or will not lock
Fuel filler door lock operates intermittently or makes no noise when operated
Difficulty refuelling, especially on vehicles that keep the door locked until the tank is released
Other readiness monitors, such as the evaporative system, may not complete

Possible causes

Signal wire shorted to earth or chafed against bodywork near the filler door or rear wheel archlikely
Faulty position switch or sensor built into the filler door lock actuatorlikely
Corroded, wet or damaged connector at the lock actuator or in-line connectorslikely
Seized or damaged lock actuator or mechanism causing an out-of-range readingpossible
Open circuit in the supply or reference feed, pulling the signal lowpossible
Fault in the controlling module or its internal driverrare

How to diagnose

Read all stored and pending codes and note the freeze frame data, looking for related lock, body control or fuel system faults
Operate the filler door and lock by hand and by the normal release, and note whether it moves freely and whether it is stuck
Visually inspect the actuator, wiring and connectors near the filler door for water ingress, corrosion, pinched or chafed wires
Check the relevant fuses and the supply and earth to the actuator using the model's wiring diagram
Watch live data for the switch or sensor state while the door is locked and unlocked, and see whether it changes
With the connector unplugged, measure the switch or sensor signal and reference voltage and test the signal wire for a short to earth
Check wire continuity and resistance between the actuator and the control unit
Check manufacturer service information for known faults on that model before condemning the module

How to fix

Repair or replace damaged, shorted or open wiring and secure it clear of sharp edges
Clean or replace corroded or damaged connectors and seal them against water
Replace the filler door lock actuator or position switch if it fails testing
Free or repair the lock mechanism if it is binding or damaged
Replace or reprogram the control module only after the wiring and actuator are proven good and the manufacturer procedure calls for it

Can I keep driving?

Low severity

The car can normally be driven, as this fault does not directly affect engine running or safety. Book it in soon, as you may have trouble refuelling if the door is stuck locked and the fault light will stay on.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.