I have a 2005 Polaris Trail Boss and when I started it the other day the engine temp light and cooler fan came on immediately. Turned it off and the fan continued to run until the battery died. Replaced the battery and tried to start and the ECM started smoking. Is this just a bad ECM or do I have other issues with the cooling fan? Thanks

 

Ecm symptoms. Fans would keep running on some,others charging problems and wiring could get hot and reports about some models catching fire. That's what the recall was all about,but the 330 wasn't on it although it should have been.Polaris Industries Expands Recall of ATVs Due to Fire Hazard | CPSC.gov This is the updated one for your model.Genuine 2005 2006 Polaris Trail Boss Magnum ATV Superpower ECM Kit | eBay

 

Replaced the ECM and the original issue was resolved. Been a few months and it's been running great until today. Cooler fan is coming on often and when the 4-wheeler was turned off it would not restart, wouldn't even turn over. Temperature light was not on. The next morning it started fine. Any ideas??

 

Pull the oil cooler sensor connector and see if that solves it. It sends the signal to the ecm for the fan to kick on. Fans on these machines rarely kick on until they get to about 240 degrees. Imo the fans aren't needed to begin with. If you can get it running check that the ecm is charging 14 volts back to the battery.If the battery checks out,disconnecting the fan sensor doesn't help the problem on starting,then the newish ecm may have crapped out.