P2780: Downshift Switch Circuit Low — what it means, the affected system and what to check before replacing parts.
Meaning, symptoms, causes and checks
P2780 reports a low electrical signal in the downshift request switch circuit. The code does not confirm that a downshift was performed or identify the faulty part.
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: P2780-00, P278000 (some scan tools add the fault-type byte, e.g. -00).