P04C8: fuel-door open-request switch reports an invalid signal

P04C8 concerns the fuel-fill door open-request sensor or switch in the cited GM hybrid table. The input is the request to open the door. It is not feedback proving that the door opened or that its lock released.

Trace the request before blaming the actuator

The monitor checks an invalid intermediate band of the reported switch signal. Separate rows handle a low or high request-circuit result. Consequently, a switch can provide an unusable request even when its value is not at an obvious electrical extreme.

The table describes the invalid band as a circuit-resistance concern, but does not provide a direct resistance measurement or connector location. Its percentage is a controller-level reading. Vehicle-specific information is needed to translate that finding into a physical circuit test.

The request also affects wake-up interpretation

The same page excludes active P04C8 when evaluating a separate fuel-door request wake-up disagreement. An invalid request input can therefore prevent a meaningful comparison with the wake-up circuit. That is a reason to retain companion codes and diagnostic availability, not to infer a second module failure.

P04C8 uses six failing samples out of eight at half-second intervals with its calibration enabled. A single button operation and a cleared code do not establish that the request channel remained valid.

Record the driver's request, the corresponding scan input and whether the controller progressed to an unlock command. This separates request detection from downstream lock performance without assuming which component failed.

Application limits

Document-level 2015 GM diagnostic table; per-code vehicle/engine/calibration applicability not established.

Source

15OBDG01 Hybrid Diagnostics, physical PDF pages 595.