P04C8: Fuel Fill Door Open Request Sensor or Switch Circuit

What it means

A general circuit fault is detected on the open-request input - the button or switch the driver presses to release the fuel fill door. The ECU loses the request signal, so motorised release becomes unavailable.

How it works

The fuel-fill door open-request switch sends an input to the control module when you press the release button. P04C8 sets when the module detects a general electrical fault in that input circuit and can no longer reliably read the request.

Common causes

Most likely first.

1. Open or short in switch wiring
2. Loose or corroded switch connector
3. Failed open-request switch

Symptoms

• Fuel-fill door may not release when requested
• Open-request button may not respond

How to diagnose it

1. Use a scan tool to record freeze-frame data and check the live open-request status while pressing and releasing the button.
2. Inspect the button and its connector for looseness, corrosion, moisture, or damage that could interrupt the input.
3. Follow the open-request wiring to the control module and look for breaks, pinched sections, or damaged insulation.
4. With the circuit diagram, check the switch and wiring for continuity and unintended shorts, isolating sections as needed.
5. If the wiring and switch test correctly, check the input at the control module and verify the circuit against the manufacturer's specification.

Common fixes

• Reconnect or clean a loose or corroded switch connector.
• Repair damaged wiring or terminals in the open-request circuit.
• Replace a failed fuel-fill door open-request switch.

Can I keep driving?

If the door releases normally, you can generally keep driving, but make sure you can access the fuel filler before a trip. The fault can leave you unable to open the door when refuelling.