Line Pressure Control during Low Loading

In D or S under low engine load condition after warming up the engine and in all ranges (P, R, N, D, or S) under the low ATF temperature condition, the PCM operates line pressure solenoid valve A, and switches the line pressure to a pressure that is lower than normal. This operation can reduce the friction in the transmission.

Fig 1: Vehicle Speed And Engine Torque Graph

Courtesy of AMERICAN HONDA MOTOR CO., INC.

The PCM turns line pressure solenoid valve A on, and applies the hydraulic pressure to the PLA' cavity on the main regulator valve. When hydraulic pressure is applied to the PLA' cavity, the main regulator valve is pushed to the spring side. This operation reduces the drain port of the main regulator valve, and causes the line pressure to be lower than normal.

Fig 2: Identifying Hydraulic Pressure Operation

Courtesy of AMERICAN HONDA MOTOR CO., INC.