Diagnostic article Generic OBD-II
P04B8: fuel-door position has entered an invalid signal band
The 2015 GM hybrid P04B8 table distinguishes an invalid fuel-door position band from separate low and high circuit diagnoses.
Read before applying this article
Documented application
Document-level 2015 GM diagnostic table; per-code vehicle/engine/calibration applicability not established.
The code alone does not identify a failed part or establish that a vehicle is safe to drive. Confirm the vehicle, reporting module and applicable service procedure.
P04B8 in the cited GM hybrid table means the fuel-fill door position signal lies in an invalid range. This is the door-position sensor or switch channel, not the separate lock-position feedback and not the driver's open-request switch.
Invalid does not mean simply open or closed
The table uses a reported-position percentage and identifies a middle signal band as invalid. Separate neighboring diagnostics cover excessively low and high readings. A value inside the overall numerical display range can therefore be electrically implausible even though it is neither near zero nor at the maximum.
That percentage should not be interpreted as the physical angle of the fuel door. The summary describes the controller's reported signal and does not supply a conversion to hinge travel or a resistance specification for a handheld meter.
Persistence matters
The published monitor requires six failing samples out of eight, sampled every half-second, and its diagnostic calibration must be enabled. A single unusual update is not the complete detection criterion. The table also describes a two-trip reporting classification for this row.
A useful diagnostic record preserves the signal channel name, the invalid-band behavior over time and any companion low/high or lock-position codes. Those details help distinguish an unstable reading from an actual door-state problem.
The summary establishes how the result is recognized, not which connector or switch has failed. Confirm the exact vehicle, circuit and service procedure before selecting parts.
Application limits
Document-level 2015 GM diagnostic table; per-code vehicle/engine/calibration applicability not established.
Source
15OBDG01 Hybrid Diagnostics, physical PDF pages 593.
Article source documents
Source checks describe how the text was prepared; they do not certify a diagnosis or confirm compatibility with every vehicle using this code.
Original code reference
Dictionary definition
Fuel Fill Door Position Sensor/Switch Circuit
This definition retains its original catalog scope. The article above is limited to its explicitly documented application.
Reference scope
Generic OBD-II definition.
A manufacturer label does not establish the model, year, engine or module to which a diagnosis applies. Read the safety and diagnostic limits.
Definition source
- DTC Database: pinned community code definitions
Source checked · MIT