P2779: Downshift Switch Circuit Range/Performance — what it means, the affected system and what to check before replacing parts.
Meaning, symptoms, causes and checks
P2779 reports that the manual downshift request switch signal or response is outside the expected range or behaviour. This is a circuit/selection indication, not proof of a particular mechanical gear engagement.
Affected system: Powertrain
Symptoms
- Warning light may illuminate
- Related system function may be impaired
- Vehicle-specific symptoms vary
Possible causes
- Transmission fluid, hydraulic, solenoid, connector, or control-circuit issue
- Related wiring, connector, power or ground fault
- Vehicle-specific mechanical or control issue
What to check
- Record stored and pending codes and freeze-frame data
- Compare commanded and actual transmission data, inspect fluid condition and level according to the vehicle procedure, then test the relevant circuit and solenoid.
- Confirm measured values against the vehicle service information
- Retest under the conditions that set the code
- Compare commanded and actual transmission data, inspect fluid condition and level according to the vehicle procedure, then test the relevant circuit and solenoid.
- Repair the verified cause and confirm the code does not return
Also written as: P2779-00, P277900 (some scan tools add the fault-type byte, e.g. -00).