I am having a problem with my 2004.5 Sportsman 500 that I can’t seem to correct. After the bike gets warmed up, the "HOT ENGINE" warning will intermittently flash on the speedometer. There is no evidence that the bike is overheating – sometimes the fan will kick in while the display is flashing "HOT ENGINE" and other times it won’t. At this point, unplugging the thermistor will always trigger the fan to turn on. The thermistor resistance is always well above where it should be for the hot engine. Thermostat has been changed, ECM has been changed, water pump impeller has been checked, thermistor has been checked in a pot of water, air has been bled from rad. Wiring harnesses have been inspected from speedometer,ecm,thermistor,fan. The only other thing is that this began happening after the fan was replaced with an aftermarket unit. Is it possible that the fan is not compatible with the ECM? I know unplugging the fan motor also causes the light to come on. Any help would be appreciated