Fashionable torque converters use electro hydraulic control for your lock-up clutch. The hydraulic circuit which locks/unlocks the torque converter clutch is managed working with hydraulic valves. The valves are actuated immediately or indirectly by solenoids. The control of the oil pressure from the lock-up clutch is done by two valves: https://torque-converter-clutch05924.blogrenanda.com/40279040/how-torque-converter-clutch-can-save-you-time-stress-and-money