#6 Checkball (Low Reverse Band Apply and Reduce)
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.
The #6 checkball is located in the valve body. The checkball is unseated by Low & Reverse reduce fluid. This allows fluid to enter the Low & Reverse band apply circuit. Low & Reverse band apply fluid is then routed to the Low & Reverse servo piston where the fluid actuates the piston and applies the Low & Reverse band assembly.