P26E9: Supply D high describes an HSO8 shutdown-state failure

For P26E9, the documented transmission controller tests whether HSO8 remains high after being disabled. Voltage above 70% of the battery level for at least 60 ms is the listed failure. The check is aimed at an off-state switch behavior, not simply a high voltage on an intentionally energized supply.

Follow the event across the power cycle

The controller saves the failure during shutdown and reports it at the next startup. Retaining the prior powerdown context is therefore more useful than assuming the condition began when the code became visible. The battery must change by less than 1.5 V during the test, and P0882 or P0883 disables it.

Interpret the output identity correctly

HSO8 is the source’s mapping for generic actuator supply D in this controller. It is not a universal label for one physical actuator across all transmissions. Applicable circuit documentation is needed before locating the load or output stage.

Verification should establish whether an eligible subsequent shutdown reaches the expected disabled-output state. A successful running command alone does not repeat that test. The source classifies a high-side switch-path concern but does not supply enough evidence to choose a replacement controller or attached component.

Document scope and source

2025 GM 25OBDG07A Part 2 documented monitor only; its application-matrix filename join is unresolved. No model, engine or universal calibration applicability is inferred. 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 938.