I know this has been posted before. But spring seems to be the time of year it happens.
Went to get coach out of storage, Did normal push on D but no go. Then I pushed real hard, Trans shifted in to D.
Got home exercised sw, still had to push hard. I did not like the idea that I could get stuck not being able to get into gear if the switch got inoperable. Check internet for possible repairs. Most pointed to sending control module to a shop for repair. :hThen I seem to remember a blog for long-ago about taking the thing apart and cleaning the PC board sw contact area.
This is not for the faint of heart, as if you screw it up the coach is stuck until the rescue squad shows up.
I removed the module form the coach being sure not to damage the plugs or pins. On my unit there are 4 long screw that hold the sw module on the control module. Removed the sw assy being careful not to damage wire ribbon/connector. Remove back cover and switch pc board. The switch contact area for D and the shift down arrow had little black specks on them. Cleaned with soft pencil eraser and alcohol. Cleaned the soft rubber contractor. Reassembled and installed. WALA now works as it has for the past 20 years.:)
This is not a fix for any code that show up just switch operation.