Diagnostic article Generic OBD-II
P04C4: fuel-door lock feedback changed without an unlock command
The 2015 GM P04C4 monitor checks an unexpected transition from locked to not locked, rather than failure to obey an unlock request.
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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.
P04C4 is a lock-position plausibility result in the cited GM hybrid summary. The previous state was locked, the current state is not locked, and the controller has not commanded an unlock. The unexpected change is the important evidence.
Preserve the sequence of states
A snapshot showing “not locked” is insufficient to explain this monitor. The controller's decision depends on the earlier locked state and absence of an unlock command. Recording only the final display would omit two parts of the diagnostic condition.
This differs from P04C0, where an actual unlock command fails to produce the expected transition. Here, the problem is a reported release without that command. The two results should not be treated as interchangeable actuator failures.
Circuit validity is a prerequisite
The table excludes related driver and lock-position electrical faults. It also uses a repeated-sample decision: sixteen failures out of twenty samples taken at 50-millisecond intervals. The monitor is therefore looking for a sustained inconsistency rather than one isolated state update.
The summary does not distinguish an actual unintended mechanical release from erroneous position feedback. That distinction requires the vehicle-specific inspection and a comparison between physical state, command history and reported state.
After any repair, verify the relevant sequence under valid diagnostic conditions. Merely demonstrating that the fuel door can open and close once does not establish that the lock-position signal remains coherent while no unlock is requested.
Application limits
Document-level 2015 GM diagnostic table; per-code vehicle/engine/calibration applicability not established.
Source
15OBDG01 Hybrid Diagnostics, physical PDF pages 594.
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 Lock Position Sensor/Switch Circuit Range/Performance
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