A torque converter pulse modulation solenoid/TCC PWM solenoid activates the torque converter lockup clutch by receiving a series of electrical pulses from the ECU. If it does not work correctly, then TCC clutch will not operate properly, resulting in poor engine performance and the possibility of engine stalling. In addition, a P1866 DTC will be stored.
How Serious is the Code?
Having a P1866 diagnostic trouble code isn’t the end of the world. But it will eventually affect the drivability of your vehicle. If there is an issue with the circuit that the TCC PWM solenoid operates on (whether electrical or hydraulic), the torque converter will not be able to operate as intended. If left untreated, these transmission problems can result in serious drivability and safety issues.
Symptoms of a P1866 include:
- Engine stalling
- Poor engine performance
- Failed upshifts/downshifts
- Transmission overheating
- Failed TCC PWM solenoid
- Dirty transmission fluid/filter
- Clogged hydraulic passage inside the transmission
How to Diagnose the Code?
When diagnosing a P1866 OBDii diagnostic trouble code, it’s important to first consider the condition of the transmission fluid, as that can have a serious impact on the operation of this solenoid. If there are no issues found with the condition of the ATF, then electrical tests will need to be performed on the torque converter PWM solenoid to determine if it is functioning properly.
What Repairs Will Fix P1866?
- Change the transmission fluid and filter
- Replace the TCC PWM solenoid
P1860 – TCC PWM Solenoid Circuit Electrical OBD-II Trouble Code