P27C0: Shift valve two circuit-high has a shutdown cross-circuit check too

P27C0 is not limited to one voltage snapshot. The cited transmission assigns it to synchronizer actuation valve two and documents both an active-output electrical check and a shutdown test for an unwanted connection to another low-side output.

Active and shutdown evidence differ

While the valve is commanded on, the driver evaluates a supply-dependent voltage limit and current-estimation error. The table includes relative and absolute current-error branches, so the DTC can summarize more than a simple fixed high voltage.

At shutdown, outputs are enabled in sequence. If one disabled output reports a ground-like state when another is enabled, and the behavior reverses when their commands swap, the controller identifies a possible connection between them. It stores that result and reports it at the next startup.

Keep the event origin

A startup indication can therefore describe the previous shutdown. Preserve whether the failure came from continuous operation or the retained cross-circuit test, along with the paired output information. The code alone does not identify which neighboring circuit is involved. Applicable service procedures must resolve the physical valve mapping and isolation method before a component is selected for repair.

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 926, GM physical PDF page 927, GM physical PDF page 940.