I was out plowing snow with my '03 600 the other day. After about 30 minutes I happened to notice the engine coolant light flashing. It's hard to say how long it was flashing. I shut off the engine and noticed the fan wasn't running. I don't know for sure if it had been running at all while plowing. I checked the radiator fins and everything looked clean in front and back. The coolant level in the overflow tank was a little about the max mark...I don't remember if it's usually this high when running. So I just let it sit for a couple hours - plenty of time for the engine to get cold in 20 degree weather. When I started it back up, the light was still flashing. Anyone have any ideas what this could be? Faulty temp sensor? Is there any way I can actually test to see if the radiator fan is working?

Thanks.