P04B9: fuel-door position feedback is below its allowed range

P04B9 concerns a low signal on the fuel-fill door position sensor/switch channel in the cited 2015 GM hybrid table. The strategy describes a short-to-ground check and evaluates a reported-position value below its calibrated threshold.

Identify which position channel is low

Fuel-door position and fuel-door lock position are separate inputs in this document. P04B9 belongs to the door-position channel; a lock-position low result has its own code. Keeping those channels distinct prevents an investigation from being directed at the wrong switch.

The table's percentage is a processed position reading. It is not a voltage specification for probing an unidentified terminal, nor a statement that the door is physically a particular percentage open.

A diagnostic category is not a proven short location

The low result is consistent with the monitored electrical fault class, but the summary does not localize a short to the sensor or harness. The vehicle-specific wiring test must establish that distinction. A mechanically closed door alone does not explain why the signal entered an invalid low band.

Detection requires repeated failed samples and an enabled calibration. Capture a short trace or the available fault data rather than relying only on a single value after the door has been moved.

For verification, confirm that the correct input remains in a valid state through the applicable operation and that the monitor completes. A cleared code or a door that opens once does not establish electrical integrity.

Application limits

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

Source

15OBDG01 Hybrid Diagnostics, physical PDF pages 593.