Reverse Input Clutch Piston
WARNING: This page is about a different car, the 2008 Isuzu i-370, 2008 Isuzu i-290, 2008 GMC Canyon, and 2008 Chevrolet Colorado. However, it is still accessible from the selected car via links, so may be relevant.
Reverse input fluid pressure moves the piston to apply the reverse input clutch plates and obtain Reverse.