P04C9

What it means

P04C9 means the control unit has judged the fuel fill door open request switch or sensor to be performing incorrectly or stuck in the off state. The request input does not change, or does not agree with other inputs such as door status or tank pressure, when it should. How the fuel door request works varies by model, so confirm the system layout for the vehicle.

Symptoms

• Fuel filler door will not open when the request button is pressed
• Warning light on, which may be the MIL or a fuel system or hybrid system warning, depending on model
• Difficulty refuelling, or the door only opens by manual release
• Fuel door button feels dead or intermittent
• Other stored EVAP or fuel tank pressure codes alongside it

Possible causes

• Faulty fuel fill door request switch or buttonlikely
• Damaged wiring, corrosion or poor connection in the switch circuit (open circuit, high resistance, short)likely
• Fuel door lock or release actuator fault causing implausible feedbackpossible
• Moisture or dirt contamination in the switch or its connectorpossible
• Fault in the body control module or other controller that reads the request signal, or a software issuerare
• Tank pressure sensor or pressure release valve fault on pressurised tank systems, if the vehicle uses onerare

How to diagnose

1. Read all stored codes and freeze frame data, and note whether any EVAP, fuel tank pressure or body control codes are also set
2. Check the fuel door request button operation by pressing it and watching the switch state in live data, if available
3. Inspect the switch, wiring and connectors for damage, corrosion, water ingress or loose pins
4. Check the manufacturer's wiring diagram, then test the switch circuit for supply, ground and signal, and measure resistance across the switch in both states
5. Operate the fuel door lock or release actuator and check it moves freely and its feedback is correct
6. On pressurised tank vehicles, check tank pressure readings and the pressure release function against model-specific procedures
7. Check for software updates or technical bulletins for the controller concerned, then clear the code and road test to see if it returns

How to fix

• Replace the faulty fuel fill door request switch
• Repair or replace damaged wiring and clean or replace corroded connectors
• Replace or repair a faulty fuel door lock or release actuator
• Dry out and clean a contaminated switch assembly, or replace it if it is damaged
• Replace or reprogram the controller only after confirming it is at fault, and apply an updated calibration if a known fault exists

Can I keep driving?

Nearby codes

• P04C8GenericFuel Fill Door Open Request Sensor/Switch Circuit
• P04CAGenericFuel Fill Door Open Request Sensor/Switch Circuit Low