Lock-up and Select Control: Notes

WARNING: This page is about a different car, the 2009 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 engaged to eliminate torque converter slip to increase power transmission efficiency.
The torque converter clutch control valve operation is controlled by the torque converter clutch solenoid valve, which is controlled by a signal from TCM. The torque converter clutch control valve engages or releases the torque converter clutch piston.
When shifting between "N" ("P") "D" ("R"), torque converter clutch solenoid controls engagement power of forward clutch and reverse brake.
The lock-up applied gear range was expanded by locking up the torque converter at a lower vehicle speed than conventional CVT models.

Fig 1: Vehicle Speed Graph

Courtesy of NISSAN MOTOR CO., U.S.A.