Diagnostic article Generic OBD-II
P2779: Downshift plausibility rejects a value that fits neither switch state
P2779 evaluates the downshift input’s valid-state windows rather than assuming a long press or a failed switch.
Read before applying this article
Documented application
2025 GM 25OBDG07A Part 2 documented monitor only; its application-matrix filename join is unresolved. No model, engine or universal calibration applicability is inferred.
The code alone does not identify a failed part or establish that a vehicle is safe to drive. Confirm the vehicle, reporting module and applicable service procedure.
P2779 is the downshift-paddle plausibility monitor in this GM transmission file. Its failure requires the analog input to be outside the accepted pressed window and outside the released window. The issue is an unrecognizable switch state, not merely a command to shift down.
The electrical check comes first
The routine requires no separate electrical fault for the paddle-minus input. That allows it to evaluate values that may avoid an extreme circuit-high or circuit-low fault yet still fail the state windows. The confirmation period, continued onto the next page, is two seconds.
The source also requires normal application operation, with neither error nor bypass state active. Those conditions matter when a fault disappears after a controller reset without a completed reevaluation.
Observe more than the final state
A useful record follows the analog value and recognized switch state during operation and release. A brief state display can miss a sustained intermediate value. The source references calibration-specific windows, which are not invented here.
P2779 should also be distinguished from the separate monitor for a paddle remaining pressed too long. Applicable service data is needed to determine why the input cannot represent either valid state and to isolate the circuit before replacing a 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.
Article source documents
Source checks describe how the text was prepared; they do not certify a diagnosis or confirm compatibility with every vehicle using this code.
Original code reference
Dictionary definition
Downshift Switch Circuit Range/Performance
This definition retains its original catalog scope. The article above is limited to its explicitly documented application.
Reference scope
Generic OBD-II definition.
A manufacturer label does not establish the model, year, engine or module to which a diagnosis applies. Read the safety and diagnostic limits.
Definition source
- DTC Database: pinned community code definitions
Source checked · MIT