Originally Posted by Wiki

the TCC,, torque converter clutch,,,, used on tree speed transmission in the 80's GM and on 4 speed automatics, the solenoid reads the speed of the transmission (car) and sends the signal to the computer which identifies that the car has reached proper crusing speed and is not under heavey load (full throttle) it then "locK" the torque converter to not allow any slippage like a standard automatic torque converter, basically making the torque converter act like a clutch,,, thus the name TCC torque converter clutch hope that helps,,

Originally Posted by ZZebes

You have a TCC Solenoid that controls the flow of fluid into the torque converter "fluid Circuit" and when the PCM commands lock up it opens the solenoid and allows pressurized fluid to flow in behind the torque Converter Clutch and applying it to the TCC Case with an enourmous amout of pressure thus locking the engine and trans together as in a standard transmission setup