P04CB code meaning
Fuel Fill Door Open Request Sensor/Switch Circuit High
Powertrain system Generic code P04xx codes Check engine light
What P04CB means
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.
P04CB at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyEasy, DIY possible
- Typical labor0.3 to 1.5 hours
- Clears after repairAfter a drive cycle
Symptoms of P04CB
- Fuel button has no effect, door does not open
- Refuelling system message in the instrument cluster
- Refuelling only via emergency release
Common causes of P04CB
- Most likelyButton line shorted to positive
- PossibleFuel button faulty
- PossibleConnector or wiring damaged
- Less likelyModule
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Fuel door open request switchSwitch wiringEngine control module
What each part of P04CB means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 4 | Area: auxiliary emission controls (catalytic converter, EGR, EVAP). |
| CB | The exact fault in that area. |
What to do next
- Note P04CB and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P04CB
What does P04CB mean?
P04CB means "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). It is a generic code, so it means the same on every make.
Is it safe to drive with P04CB?
Usually yes, for a short time, if the check engine light is steady and the car drives normally. If the light flashes or the car runs badly, stop and have it checked.
Will P04CB fail an emissions test?
Yes, it can. P04CB is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P04CB to fix?
Difficulty: easy. A typical repair takes 0.3 to 1.5 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will P04CB clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.