Line Pressure Control is Based On The TCM Line Pressure Characteristic Pattern

WARNING: This page is about a different car, the 2008 Infiniti EX35. However, it is still accessible from the selected car via links, so may be relevant.

The TCM has stored in memory a number of patterns for the optimum line pressure characteristic for the driving state.
In order to obtain the most appropriate line pressure characteristic to meet the current driving state, the TCM controls the line pressure solenoid current value and thus controls the line pressure.

Normal Control

Each clutch is adjusted to the necessary pressure to match the engine drive force.

Fig 1: Line Pressure Characteristic -- Normal Conditions
Courtesy of NISSAN MOTOR CO., U.S.A.

Back-up Control (Engine Brake)

When the select operation is performed during driving and the A/T is shifted down, the line pressure is set according to the vehicle speed.

Fig 2: Line Pressure Characteristic -- Back-Up Control
Courtesy of NISSAN MOTOR CO., U.S.A.

During Shift Change

The necessary and adequate line pressure for shift change is set. For this reason, line pressure pattern setting corresponds to input torque and gearshift selection. Also, line pressure characteristic corresponds to engine speed, during engine brake operation.

Fig 3: Line Pressure Characteristic - During Shift Change
Courtesy of NISSAN MOTOR CO., U.S.A.

At Low Fluid Temperature

When the A/T fluid temperature drops below the prescribed temperature, in order to speed up the action of each friction element, the line pressure is set higher than the normal line pressure characteristic.

Fig 4: Line Pressure Characteristic -- At Low Fluid Temperature
Courtesy of NISSAN MOTOR CO., U.S.A.