Modern torque converters use electro hydraulic Management for your lock-up clutch. The hydraulic circuit which locks/unlocks the torque converter clutch is managed making use of hydraulic valves. The valves are actuated right or indirectly by solenoids. Visible Inspection:  Start with a basic visual inspection. Search for any indications of leaks https://torque-converter-clutch03578.yomoblog.com/40566770/torque-converter-clutch-things-to-know-before-you-buy