What does it mean?
P1779 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Incorrect or Invalid Torque Signal to the TCM .
Symptoms
- MIL (check engine lamp) is on with communication or engine codes stored alongside
- Very harsh upshifts under load, because the engine no longer reduces torque during the shift
- Shift shock felt through the whole vehicle when accelerating
- Transmission drops into limp mode with a fixed gear
- Flare between gears at higher throttle openings
- Other modules may show lost-communication codes at the same time
Likely causes
- Engine control module transmitting a wrong or absent torque value because of its own input faults
- Data bus fault between the two modules: broken wire, corroded pin, or a damaged terminating resistor
- Engine sensor problems such as air mass, throttle or crankshaft position skewing the calculated torque
- Software or calibration mismatch after one of the modules was replaced or reprogrammed
- Low battery voltage or poor module grounds causing brief module dropouts
- Interference from an aftermarket device or tuning box spliced into the bus
- Failed engine or transmission control module
How to fix it
- Scan all modules and repair engine performance and communication codes first
- Compare the torque value the transmission module reports with the value the engine module is sending
- Inspect the bus wiring and connectors between the two modules and measure bus resistance with the ignition off
- Check battery condition, charging voltage and all module ground points with a voltage drop test
- Confirm both modules hold compatible, up-to-date calibrations and update if a revision exists
- Remove any aftermarket device connected to the bus and retest before replacing a module