2-3 Shift Valve

The 2-3 shift valve automatically controls shifts between second and third gear by switching shift solenoid A on/off.
In second gear position, with shift solenoid A on, passage A line pressure is drained and the passage to the direct clutch is closed. The passage A line pressure causes the valve to shift by switching shift solenoid A off, and the passage to the direct clutch is opened, engaging third gear.

Fig 1: 2-3 Shift Valve Operation
Courtesy of MAZDA MOTORS CORP.