A/T Fluid Pressure Manual Valve Position Switch (TFP Val. Position Sw.) Assembly
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 through the 1-2 shift valve and to the TFP Val. Position Sw. Assembly, which signals the PCM that the transmission is in Reverse position.