Line-Pressure Control During Shifting

The line pressure which engages shift clutches to create 1st to 4th speeds is controlled by the TCM to meet varying operating conditions.

During gear shifting, the TCM decreases the line pressure to a level that matches the selected gear in order to minimize shifting shock loads.

Fig 1: Line-Pressure Control During Shifting Chart

Courtesy of SUBARU OF AMERICA, INC.

During gear shifting, the TCM controls the line pressure as follows: 

• The TCM receives signals such as throttle position signal and accelerator pedal speed signal. Based on these input signals, it issues a control signal to the line pressure duty solenoid.
• The pressure from the line pressure duty solenoid (line pressure duty pressure) is converted by the pressure modifier valve into a modifier pressure, and the modifier pressure is applied to the pressure regulator valve.
• The pressure regulator valve adjusts the oil-pump-generated line pressure according to the modifier pressure to make the line pressure match to the driving condition.