Lock-Up Control: Notes
WARNING: This page is about a different car, the 2002 Nissan Sentra. However, it is still accessible from the selected car via links, so may be relevant.
The torque converter clutch piston in the torque converter is locked to eliminate torque converter slip to increase power transmission efficiency. The solenoid valve is controlled by an ON-OFF duty signal sent from the TCM. The signal is converted to an oil pressure signal which controls the lock-up piston.