My 2016 GMC Sierra with the 5.3L has done the fan on high for 3 straight years. I live in Michigan and the only time the fan turns onto high is in the Spring and Fall time periods when we temperatures between 40F & 60F degrees. So any time its in the 40's or 50's it seems to happen, then in the winter when its teens, 20's and 30's it never turns on. The same goes for the summer when its 70's, 80's, 90's it never turns on. I have replaced my coolant sensor with an AC Delco OEM unit. I disconnected the battery for 10 minutes and the problem temporarily went away, but came back two days later. Next I've purchased a thermostat, I plan to change it out this week. I am slowly doing one thing at a time to see what the root cause was for my situation to hopefully help the next person. I have no codes being thrown, there is no check engine light coming on.
