First Gear (D Range): Operation

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With shift solenoids A, B, and C ON, pilot pressure is applied to every bottom end of the shift valves, and each shift valve is positioned on the upper side.
Line pressure is applied the low clutch accumulator, and engages the low clutch through shift valve B.
Line pressure is applied reduction brake through shift valve B.
Line pressure delivered to the pressure regulator valve is sent to the torque converter through the TCC control valve as torque converter pressure.

Fig 1: Identifying First Gear (D Range) Line Pressures
Courtesy of MAZDA MOTORS CORP.