P257D: Hood-switch signal falls into an invalid intermediate range

P257D checks hood-switch signal rationality in the reviewed GM monitor. It identifies a value that does not correspond to an accepted switch state, rather than simply reporting that the hood is open.

Switch type determines the invalid band

The row selects the Global A switch type, for which the invalid range is 43.4% to 45.7%. It also documents a Global B alternative with an invalid range of 59.34% to 66.96%. These are signal percentages used by the diagnostic, not percentages of physical hood opening.

Applying the wrong switch-type band could reverse the interpretation of a recorded value. Confirm the vehicle's configured switch type and parameter scaling before using the limits.

Persistent invalid state versus a transition

The controller requires 80 failing samples in 100 total, evaluated on a 12.5-millisecond loop. The row uses run/crank as an enable condition for the documented configuration. A fleeting intermediate reading during a state change is therefore different evidence from an invalid value persisting through the diagnostic window.

Record actual hood state and signal behavior together using the applicable procedure. The monitor identifies an implausible electrical representation; it does not prove that the latch is mechanically secure or establish which part of the circuit failed.

Verification should show valid, appropriately changing switch states and completion of the enabled monitor without recurrence. The source lists Type B, two-trip behavior, without providing a switch location, pinout or replacement instruction.

Source and applicability

Confirm the reporting module, system and calibration before applying these diagnostic limits. GM diagnostic table, PDF page 659.