The main function of the toque converter clutch or TCC solenoid is to send pressurized fluid to the torque converter’s clutch allowing it to achieve lock up in 4th gear based on a signal from the engine control module (ECM). The valve opens allowing for fluid to apply the TCC, and when the signal stops, the fluid is then vented out which will then disengage the clutch.
Until engine temps reach a certain point, the TCC solenoid will not allow for lock up.
In essence, the TCC solenoid is like a computer controlled on and off switch for your 4l60e’s torque converter lock up.