System Description

WARNING: This page is about a different car, the 2019 Nissan NV3500 HD and 2019 Nissan NV2500 HD. 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.
Lock-up operation, however, is prohibited when A/T fluid temperature is too low.
The torque converter clutch control valve operation is controlled by the torque converter clutch solenoid valve, which is controlled by a signal from TCM, and the torque converter clutch control valve engages or releases the torque converter clutch piston.

Courtesy of NISSAN NORTH AMERICA, INC.

Lock-up Operation Condition Table

Selector lever	"D" position						"M" position
Gear position	7	6	5	4	3	2	7	6	5	4	3	2
Lock-up	x	-	-	-	-	-	x	x	x	x	x	x
Slip lock-up	x	x	x	x	x	x	x	x	x	x	x	x

Lock-up released

In the lock-up released state, the torque converter clutch control valve is set into the unlocked state by the torque converter clutch solenoid and the lock-up apply pressure is drained.
in this way, the torque converter clutch piston is not coupled.

Lock-up Applied

In the lock-up applied state, the torque converter clutch control valve is set into the locked state by the torque converter clutch solenoid and lock-up apply pressure is generated.
In this way, the torque converter clutch piston is pressed and coupled.