Intermittently shutting down and low coolant warning

[Ambenjudah]

I even tried submerging the coolant sensor in a jug of water. Still didn't help, I didn't think it would. These sensors aren't actually submerged in coolant, to be honest, I have no idea how they're supposed to work. They fit up into a niche in the reservoir and never actually contact the coolant itself. I went thru the diagnostic checks again and I get down to where it says: replace ecm...but Cummins tested it and it came back good. I don't know if I have another truck here with a similar ecm to swap it out with, I'll have to look.