Reverse Band Assembly (615)
WARNING: This page is about a different car, the 2008 Buick LaCrosse and 2008 Buick Allure. However, it is still accessible from the selected car via links, so may be relevant.
Reverse fluid exhausts from the reverse servo, the #5 ball check valve unseats, allowing reverse servo fluid to quickly exhaust at the manual valve, and the reverse band releases, shifting the transmission into NEUTRAL.