P04CB: Fuel Fill Door Open Request Sensor or Switch Circuit High

What it means

Same as P04C8 with the signal voltage shorted to supply or constantly high. Wiring faults of this kind typically come from chafing, water ingress at connector seals, or pin push-back — a wiggle test on the harness while the code is active often confirms the location.

How it works

The fuel-fill door open-request switch provides an input that the control module expects to remain within a defined electrical range until the button is pressed. P04CB sets when the input is above that range, which can happen if the signal is shorted to a supply voltage.

Common causes

Most likely first.

1. Signal shorted to supply
2. Connector pins corroded - high contact resistance
3. Supply wire pinched against B+ source

Symptoms

• Fuel-fill door may release unexpectedly or fail to release
• Open-request button may not respond correctly

How to diagnose it

1. Use scan-tool live data to see whether the open-request input remains active or high with the button released.
2. Inspect the switch connector and harness for corrosion, pin damage, or a signal wire pinched against a power source.
3. Use the circuit diagram to test the signal wire for a short to supply and check connector pin fit.
4. Wiggle the harness while monitoring the input to identify a movement-sensitive short or poor connection.
5. Test the switch and module input against the manufacturer's specification if the harness has no short.

Common fixes

• Reconnect or repair corroded or damaged connector terminals.
• Repair a signal wire shorted to a supply wire or other power source.
• Replace a switch that holds the input high when released.
• Repair a verified module input fault after the circuit tests pass.

Can I keep driving?

You can generally drive if the fuel-fill door is closed and secure, but check access before refuelling. A falsely active input may cause inconsistent operation or an unintended release.