3-4 Shift Valve
WARNING: This page is about a different car, the 2009 Cadillac DTS. However, it is still accessible from the selected car via links, so may be relevant.
Spring force and D321 fluid pressure hold the 3-4 shift valve in the downshifted position. The 3-4 shift valve allows D321 fluid to pass through the valve and enter the coast clutch feed circuit. Coast clutch feed is then routed to checkball #9.