At Low Fluid Temperature

Fluid viscosity and frictional characteristics of the clutch facing change with fluid temperature. Clutch engaging or band-contacting pressure is compensated for, according to fluid temperature, to stabilize shifting quality.
The line pressure is reduced below 60°C (140°F) to prevent shifting shock due to low viscosity of automatic transmission fluid when temperature is low.

Fig 1: Line Pressure And Throttle Opening Normal Control Graph
Courtesy of NISSAN MOTOR CO., U.S.A.
Line pressure is increased to a maximum irrespective of the throttle opening when fluid temperature drops to - 10°C (14°F). This pressure rise is adopted to prevent a delay in clutch and brake operation due to extreme drop of fluid viscosity at low temperature.

Fig 2: Line Pressure And Throttle Opening Normal Control Graph
Courtesy of NISSAN MOTOR CO., U.S.A.