Reverse Inhibitor Control

When R is selected while the vehicle is moving forward, the PCM commands shift solenoid valve D to remain OFF so that shift solenoid valve D pressure (SD) is not applied to the reverse control valve. Line pressure (3) stops at the reverse control valve, and is not applied to the servo valve. No power is transmitted to the reverse direction.

Fig 1: Automatic Transmission Hydraulic Flow Diagram - Driving In Reverse Gear

Courtesy of AMERICAN HONDA MOTOR CO., INC.