Check coolant level

[CMV]

So my alternator went out and I changed it this past weekend. What a joy that was....... Anyway, after R&R the radiator to get to the alternator the DIC says check coolant level. I reset codes and it keeps coming back. Level in overflow tank is correct, temp gauge seems to work properly and holds at about halfway once the engine is hot, and I don't see or smell any coolant leak.

What did I screw up to trigger this?

It was a frustrating chore getting stuff out of the way to access the alternator and equally frustrating getting it all back in place. But I don't remember unplugging or even seeing anything that would be a coolant level sensor. 2 fan pigtails, outside air temp sensor (i think - mounted on hood latch supports), harness at alternator, and battery are only electrical connections I remember messing with.

[winterset]

The sensor is in the surge tank (the tank with the radiator cap). The level should be about 3 inches down from the top. Could it be you are a little low? Make sure your surge line is not plugged up, and coolant is flowing nto that tank fron the top hose. I know when i replaced my radiator, i too was getting the low coolant message for a little bit. I kept adding 50/50 till when i checked it cold, the coolant was at the correct level. If you do put too much n, it'll blow out of the surge tank overflow hose onto the street. (Mine released about a cup onto the driveway). Otherwise, just follow the wire for that sensor, and look for a pinched wire.