A/T Fluid Pressure Manual Valve Position Switch (TFP Val. Position Sw.) Assembly
WARNING: This page is about a different car, the 2004 Pontiac Sunfire, 2004 Chevrolet Classic, and 2004 Chevrolet Cavalier. 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.