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.
Low fluid pressure is routed to the TFP Val. Position Sw. Assembly, which signals to the PCM that the manual valve is in the Manual First position.