P27D8: Valve-five circuit high has two distinct event histories

The P27D8 implementation in this source concerns synchronizer actuation valve five. Active monitoring checks supply-dependent driver voltage and the difference between estimated and requested current. A circuit-high description therefore summarizes multiple electrical checks rather than one universal voltage threshold.

Shutdown adds another possibility

The same DTC is used when sequential low-side-output testing indicates two outputs are connected. The controller looks for a reciprocal response: a disabled output reacts when another is active, and the reverse command arrangement produces the corresponding fault. It retains that result at shutdown and reports it at the next startup.

Consequently, the time the code becomes visible may not be the time the electrical interaction was measured.

Preserve the diagnostic origin

Keep any active-driver failure details separate from the stored shutdown-pair result. A normal running valve-five signal cannot exclude a failure seen only during the cross-output sequence. Supply faults P0882 and P0883 also affect whether evaluation is available. The generic solenoid-S description requires mapping to the specific controller. This monitor summary does not identify a particular neighboring conductor or decide whether the repair belongs to the valve, harness or controller electronics.

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 929, GM physical PDF page 941.