P2780: Downshift circuit low has a printed threshold conflict to resolve

The P2780 row checks the downshift, or TAPDN, input for an electrically low value. It prints a threshold below 2,519 mV, 30 mV hysteresis and at least 150 ms confirmation. A separate page lists a pressed-paddle window starting at 2,200 mV, so the two printed ranges overlap. This remains a documented source limitation.

Electrical low is a separate question

The row evaluates voltage directly. The P2779 plausibility check instead asks whether the signal fits the accepted pressed and released states after electrical faults are excluded. Those two monitor purposes should not be collapsed into an assumption that the paddle is mechanically stuck.

The source requires eligible controller supply voltage and excludes cranking and stop-key states. P0882 or P0883 disables the low-input monitor.

Resolve the boundary before judging a reading

Retain the raw input and actual controller calibration, then consult its service specifications for the valid voltage windows. Do not use this article’s disclosed overlap as an instruction to condemn a reading in the disputed region. The DTC alone cannot distinguish a switch, connection or controller-input fault, and it supplies no universal replacement recommendation.

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 911, GM physical PDF page 949.