Pressure Regulator and Boost Valves
WARNING: This page is about a different car, the 2010 Pontiac G5 and 2010 Chevrolet Cobalt. However, it is still accessible from the selected car via links, so may be relevant.
Reverse fluid is routed to the boost valve. Reverse fluid assists torque signal fluid pressure. The addition of reverse fluid pressure increases the operating range of the line pressure in Reverse position.