What does it mean?
P1780 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Engine Torque Signal Circuit Malfunction .
Symptoms
- MIL (check engine lamp) is on and shifts become notably harsh, especially upshifts under acceleration
- A distinct thump or bang between gears
- Engine speed flares between gears at part throttle
- Transmission enters limp mode with one fixed gear
- Shift timing feels random or unrelated to how the vehicle is being driven
- Fuel consumption rises and the drive feels coarse
Likely causes
- Open or broken conductor in the torque signal wire between the engine and transmission modules
- Signal wire shorted to ground or to a voltage source along its route
- Corroded or spread terminals at either module connector
- Engine control module output driver for the torque signal failed
- Poor grounds or a weak battery causing signal levels to drift out of range
- Incorrect or mismatched module calibration after a repair
- Transmission control module input circuit fault
How to fix it
- Read all stored codes; deal with engine and charging faults first
- Back-probe the torque signal wire at the transmission module and observe it with a scope or a duty-cycle capable meter while blipping the throttle
- With both connectors disconnected, check the wire for continuity and for shorts to ground and to battery
- Perform voltage drop tests on the grounds of both modules and confirm charging voltage under load
- Inspect both module connectors for corrosion, moisture and pushed-back terminals
- Verify calibration compatibility, then reprogram or replace the module that is proven not to be producing the signal