P0659: An actuator supply high fault can be discovered during shutdown

P0659 is the actuator-supply A high code. The cited GM TCM tests high-side output 1 during powerdown, then stores a failed result in nonvolatile memory for use at the next startup. The time when the code appears may therefore differ from the time of the electrical check.

The output should fall when disabled

With the high-side output disabled, the monitor expects a defined voltage established by the circuit. If HSO1 remains above 70 percent of battery voltage, the table treats that as a shorted-switch condition. The fault confirmation time is at least 60 milliseconds.

Supply must be above 8.75 and below 18 volts, and its change during the test must remain below 1.5 volts. The shutdown test must be active; P0882 and P0883 are disabling faults.

Review the previous shutdown

A normal-looking output during the next running session does not reproduce the powerdown test. Preserve shutdown history and the stored result instead of assuming the fault arose at the instant the scanner displayed it.

The percentage boundary is relative to battery voltage, not a fixed seven-volt rule. The source does not locate the shorted path or establish which physical actuator is supplied by HSO1. The actual wiring and shutdown diagnostic procedure are needed before choosing a repair. This monitor’s stored-result behavior is essential to meaningful verification.

Source and applicability

This explanation covers the cited GM monitor, not every vehicle carrying this code. The application-matrix filename does not resolve cleanly to this file, so no model or engine fitment is assigned. GM diagnostic table, PDF page 936.