Okay I have a 06 sportsman 500 HO. Some friends and I went riding a couple weekends ago and while going up a trail, the gauge started flashing "HOT" so I turned it off and placed my hand on the radiator and it was cool as could be, like it hadn't even been running. Now I think I have general idea of what it could be and that would be the Thermostat is bad. I have washed all the mud from the radiator and that didn't fix the problem. I am wanting to get some other people's opinions about what they think it could be.

 

My guess is its that old # 4011110 Chinese ecm,if you haven't already replaced it under recall. AND if you have even the replacements have gone bad! IF its not that I would make sure the area around the fan is clean and free of any mud,this is another problem area. PLUS one other thing to try is to remove the radiator cap until fan cycles on in case of any trapped air. OPT

 

sounds like another ecm issue. check for recall if any on that model.