P2537: Accessory-line voltage disagrees with the wakeup state

P2537 is described here by the electronic brake control module, even though its generic title concerns the ignition switch accessory circuit. The monitor compares two electrical states: the run-crank wakeup line is high while the accessory line is below 2 V. That disagreement is the useful diagnostic clue.

Why context matters more than a low reading

A low accessory line on its own does not reproduce the full trigger. The controller also needs the wakeup state that makes the accessory voltage inappropriate. GM associates the result with an interruption or a short to ground, but the summary does not distinguish those possibilities by itself.

The source lists a 0.5-second check, a once-only frequency and two-trip reporting. Consequently, observing normal voltage later in the drive may miss the startup-related evaluation described by this row.

Capture the two states together

For a useful verification, retain when the brake controller woke and what the accessory input reported at that point. An engine-module ignition-status description alone is not a substitute for this local comparison. Applicable wiring information is needed to identify the actual wakeup and accessory paths. This code does not automatically identify the ignition-switch assembly as the failed component, and the table provides no universal terminal or replacement instruction.

Document scope and source

2025 GM 25OBDG03A documented EBCM monitor only. No model or engine applicability is inferred from the file-level vehicle matrix. These figures explain the cited controller logic, not a vehicle-specific repair instruction. Match the vehicle’s service information before applying them.

GM physical PDF page 37.