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

On plug-in hybrids with a sealed, pressurised tank, pressing the fuel button (open request) starts a refuelling mode: the module opens the tank valve, releases the pressure into the charcoal canister and only then unlocks the filler door via an electric actuator (Ford patent). P04CB means the button line is above its valid range. On Mitsubishi's Outlander PHEV from 2023 the engine module feeds the button and a press pulls the line to ground; P04CB sets if the line carries battery voltage for 2 s, i.e. a short to positive. Mitsubishi shows a 'refuelling system service required' message for these codes and gives no drive-cycle pattern.

Low severity. Can I keep driving?You can normally keep driving. If it affects the fuel level, do not trust the gauge and refuel earlier than usual.

Symptoms

Fuel button has no effect, door does not open
Refuelling system message in the instrument cluster
Refuelling only via emergency release

Most likely causes

Button line shorted to positive
Fuel button faulty
Connector or wiring damaged
Module

What to check, in order

Start with the simplest. You can tick off each step.

Check the connector and wiring
Check the continuity of the wire between the component and the control module.
Use live data to compare the reading with actual conditions
Measure power, ground, and signal
Replace the sensor if the circuit is good

Good to know

Repair difficulty: easy
It affects emissions.

What each character of P04CB means

P: Powertrain: engine and transmission
0: Generic code: same on every make
4: Emissions
CB: Specific fault in that system

Frequently asked questions

Can I keep driving with code P04CB?

You can normally keep driving. If it affects the fuel level, do not trust the gauge and refuel earlier than usual.

What causes code P04CB?

The most common causes are: button line shorted to positive; fuel button faulty; connector or wiring damaged.

Related codes

Sources

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.