I drive a 2007 Equinox LT, 156k on the odometer. Last week I got to work and noticed on my message center "Engine Hot, A/C Off". My coolant fans were both running full blast and my temp gauge had bottomed out, but nothing else seemed amiss. After sitting a couple hours in 36 degree weather, I came out on my break and checked the coolant tank, which was a little low (I flushed the heater core a couple weeks ago, and might not have topped off with enough coolant). I topped off the tank, then started the car and immediately got the same message, both fans blaring, so I knew it really wasn't an overheating issue. On the way home from work the message disappeared, and the temp gauge went back to its normal zone (slightly less than halfway). BTW the heater works fine too.
Obviously this is a sensor problem somewhere, but exactly which one could it be? Engine/coolant temp sensor? Could the thermostat be involved as well? Is this a common problem for this model Equinox? Just bought the car used last month, so don't know about its prior history.