Start with the switch, but don't try to take it apart unless you have tiny little fingers and love little steel balls. Usually they get dirty or the contacts pit. In either case, remove the switch, get yourself some WD-40. Fill the switch up with this and run the little actuators back and forth, up and down, etc. The idea is to try and loosen or remove any crud, etc from the contacts. Finish the job by dunking the switch in some isopropyl alcohol, shake out the excess and allow it to dry. You can force it a bit with a hair dryer. If you get function back, then one of two things will happen. It will continue to work or it will fail again, in which case you now know what the problem is and you will have to replace the switch. This has worked for me in the past with similar devices.
2000 Dodge Grand Caravan SE
No matter what you fix, there will always be something else to fix..
"Warranty" is just another way of postponing the inevitable.