CEL low temp

[Wahoo]

My CEL came on today. I stopped at the auto parts store, and had them scan it. Unfortuantly, I didn't see the code, but saw that it said low temp. This after driving 45 minutes in 90 degree heat. The parts guy said that the sensor may be going. Anyone have this happen to your 5? Where's the temp sending unit located? Is it possible to do this myself?