Fuel filler door request switch stuck or faulty, holding the signal low; Signal wire shorted to ground or chafed against bodywork; Corroded, wet or damaged connector at the switch or control unit; Water ingress or debris around the switch or filler door assembly; Faulty filler door actuator or release module affecting the circuit; Fault in the control unit input or an outdated calibration, where the manufacturer documents one.

P04CA

Fuel Fill Door Open Request 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
CA: FaultThe specific fault in that area

What it means

P04CA means the control unit has detected a low voltage signal on the circuit for the fuel filler door open request switch or sensor. This is the button or input that asks the vehicle to release the fuel filler door, often on cars with a sealed or pressurised fuel tank, such as many hybrids. The code sets when the signal sits lower than expected, which points to a short to ground, a stuck switch or a fault in the control unit input. Exact circuit layout and switch location depend on the model.

Symptoms

Fuel filler door will not open when the button is pressed
Fuel filler door opens unexpectedly or cannot be locked or released normally
Difficulty refuelling, especially on vehicles that depressurise the tank before release
Warning light on, or a fuel system or filler door message on some models
No other noticeable driveability problems

Possible causes

Fuel filler door request switch stuck or faulty, holding the signal lowlikely
Signal wire shorted to ground or chafed against bodyworklikely
Corroded, wet or damaged connector at the switch or control unitpossible
Water ingress or debris around the switch or filler door assemblypossible
Faulty filler door actuator or release module affecting the circuitpossible
Fault in the control unit input or an outdated calibration, where the manufacturer documents onerare

How to diagnose

Read all stored codes and freeze frame data, noting any related body or fuel system codes, then record and clear only after the repair so you can see if it returns
Check the switch operation by pressing it and watching the live data or switch status, if available, for a stuck or constantly low reading
Inspect the switch, filler door area and surrounding trim for damage, water, dirt or a jammed button
Inspect the wiring and connectors from the switch to the control unit for chafing, corrosion, pushed-out pins and moisture
Check the circuit reference voltage and ground at the switch connector against the manufacturer wiring diagram
With the switch disconnected, test the signal wire for a short to ground and check its continuity and resistance
Test the switch itself for correct resistance or continuity in both pressed and released positions
Check for relevant technical service bulletins or software updates for your model before condemning the control unit

How to fix

Replace the filler door request switch if it is stuck or reads out of range
Repair or replace the damaged wiring section causing the short to ground
Clean, dry and re-pin or replace corroded or damaged connectors
Fix the source of water ingress or clear debris around the switch and filler door assembly
Replace the filler door actuator or release module if testing shows it is loading the circuit
Update the control unit software only if the manufacturer lists it as a fix, or repair or replace the control unit if the input is proven faulty

Can I keep driving?

Low severity

The car can normally be driven as usual, as this fault mainly affects opening the fuel filler door. Book it in soon, particularly if you cannot refuel, and avoid forcing the door open.

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