2016 Colorado (56,000 miles) has started to intermittently show a “Service 4WD” message. Now it has stared to switch into 4WD unexpectedly while driving. When this happened I stopped and tried turning the 4WD selector. It showed 4WD High and would not change. I left the selector in 2WD and after 6 or 7 miles it switched back. The dealer has NOT been able to find anything after three days.