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.
PRND4 fluid exhausts from the TFP Val. Position Sw. Assembly, which signals to the PCM that the manual valve is in the Manual Third position.