Driving in 4th gear
The PCM turns shift solenoid valve A OFF and shift solenoid valve B ON and OFF (depending on the shift map) in 4th gear. As the speed of the vehicle reaches the programmed value, the PCM activates A/T clutch pressure control solenoid valve C, and applies CPC pressure (57) to the shift valve C pressure port (57). As the line pressure (4B) from shift valve B is not applied to shift valve C, shift valve C is moved to the right side by a spring force to connect the CPC pressure port (57) on shift valve C and the line pressure port (5B) leading to the reverse inhibitor valve. Since reverse inhibitor valve also remains on the right side under a line pressure (4), it connects the line pressure port (5B) from shift valve C on the reverse inhibitor valve to the pressure port (40) leading to the 4th clutch. With this shift valve C and the reverse inhibitor valve operations, the CPC pressure (57) flows from the reverse inhibitor valve pressure port (5B, 40) to the 4th clutch through shift valve C pressure ports (57, 5B). Then the 4th clutch is engaged by 4th clutch pressure (40). 1st clutch is also engaged, but since the rotation speed of the countershaft exceeds that of 1st gear, no power is transmitted because the one-way clutch causes 1st gear to free-wheel.