Check engine light and coolant

I recently took my truck to my mech. to flush the coolant among other things becuase it was tested at +5 (front and rear difs/transfer case fluid changed). The check engine light had turned on a few days before, and they were supposed to get the code so I knew what was going on. When i got the truck back the light didn't turn on, and they said they didn't clear or test the code. Is there any sensor for coolant level, or something in that system which would have triggered the light. And then, could flushing the coolant have fixed the problem. I was thinking no, but i don't know if there is a sensor in that area. Thanks for any help