A/T Fluid Pressure Manual Valve Position Switch (TFP Val. Position Sw.) Assembly
WARNING: This page is about a different car, the 2008 Pontiac G5 and 2008 Chevrolet Cobalt. However, it is still accessible from the selected car via links, so may be relevant.
The D21 fluid from the 2-3 shift valve is routed to the TFP Val. Position Sw. assembly, which signals to the PCM that the manual valve is in the Manual Second position.