What does it mean?
P1860 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Torque Converter Clutch PWM Solenoid Circuit Malfunction .
Symptoms
- Check engine lamp on, often with a lockup-related complaint
- Shudder or vibration at steady cruise that feels like driving over rumble strips
- Engine stalling when coming to a stop, as the converter stays locked
- No lockup at all, so cruising rpm is high and fuel consumption climbs
- Rising fluid temperature and limp mode in some cases
Likely causes
- Solenoid winding shorted or open internally, a common failure with age and heat
- Control wire shorted to ground or broken inside the transmission at the internal harness
- Fluid intrusion and corrosion at the transmission case connector
- Debris or varnish jamming the solenoid so it cannot modulate smoothly
- External harness chafed between the case connector and the module
- Contaminated or degraded fluid affecting apply pressure and solenoid operation
- Module output driver damaged, often after the solenoid has shorted
How to fix it
- Read the codes and freeze frame, then check fluid level, colour and smell carefully
- Inspect the case connector for fluid, corrosion and terminal condition, and the external harness for chafe
- Measure the solenoid resistance at the case connector and compare it with specification
- Test the control wire back to the module for opens and shorts to ground or voltage
- Command the solenoid on the scan tool and graph commanded lockup against engine and input speed on a road test
- Drop the pan, inspect the internal harness and the solenoid, and check the magnet for debris
- Replace the solenoid and service the fluid and filter, then confirm smooth lockup and release on a road test