Faulty or stuck fuel door open request switch or button; Wiring damage, chafing or short to voltage on the request switch signal circuit; Corroded, loose or water-contaminated connector at the switch or control unit; Open circuit in the signal or ground wire that causes a high reading; Fault in the control unit that monitors the switch, such as a body or fuel system module; Faulty filler door latch or actuator assembly with an integrated switch.

P04CB

Fuel Fill Door Open Request Sensor/Switch Circuit High.

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
CB: FaultThe specific fault in that area

What it means

P04CB means the control unit has seen a voltage that is too high on the circuit for the fuel filler door open request switch or sensor. This is the button or input that asks for the filler door to be released, and on some vehicles it also asks for tank pressure to be relieved before refuelling. The unit set the code because the signal sat above its expected range, which points to a short to voltage, a stuck switch or an open circuit that is read as high. How the system is laid out and which module monitors it depends on the model.

Symptoms

Warning light on, or a fuel system or hybrid system message
Fuel filler door will not open when the request button is pressed
Filler door stays released or unlocked when it should be closed
Delay or refusal to release tank pressure before refuelling on vehicles with a sealed fuel tank
Request button feels stuck or gives no response

Possible causes

Faulty or stuck fuel door open request switch or buttonlikely
Wiring damage, chafing or short to voltage on the request switch signal circuitlikely
Corroded, loose or water-contaminated connector at the switch or control unitpossible
Open circuit in the signal or ground wire that causes a high readingpossible
Fault in the control unit that monitors the switch, such as a body or fuel system modulerare
Faulty filler door latch or actuator assembly with an integrated switchrare

How to diagnose

Read all stored codes and freeze frame data, and note whether the code is current or history and whether other body or fuel system codes are present
Check the vehicle's service information for how the filler door request circuit works on this model, including whether the switch is a simple input or part of a tank pressure system
Inspect the request switch, the filler door area and the connectors for moisture, corrosion, damage or a stuck button
Look at the live data for the switch status and see whether it reads pressed when it is not, and whether it changes when the button is operated
Check the wiring between the switch and the control unit for chafing, shorts to voltage and open circuits
Measure the reference voltage, signal and ground at the switch connector against the specifications for the model
Compare the switch resistance or operation against the specification, and test or swap with a known good part if the manufacturer allows
Clear the code and road test and operate the switch several times to see whether the code returns

How to fix

Replace the fuel door open request switch or button if it is stuck or out of specification
Repair or replace the damaged wiring or any short to voltage on the signal circuit
Clean, repair or replace corroded or loose connectors and seal out moisture
Repair open circuits in the signal or ground wires
Replace the filler door latch or actuator assembly if it contains the failed switch
Repair or replace the control unit only once the switch, wiring and connectors have been proved good

Can I keep driving?

Low severity

The car can normally be driven as usual, but you may have trouble opening the filler door or refuelling, so keep enough fuel in the tank. Book it in for diagnosis soon, especially if the door will not open.

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