Replaced Thermostat, now false low coolant

[Cynthtmr]

A few weeks ago, my thermostat in the radiator was replaced. Ever since, my dash now says "low coolant" even though the coolant level is fine. I can't really find anything on other forums, so here I am...

Any suggestions on what it could be, or needs to be done? It's a 2012 GMC 2500 Denali, diesel.

I'm not super car savy, so if you can "dumb it down", help a girl out, I'd appreciate it! lol

Thanks!

Also, posting this in multiple forums... hope that's not taboo... 

[Formulabruce]

I will guess that you have a  sensor problem in the "overflow tank" /. Take a look at it, shake it, take off cap when cooled off and it may need a good flushing out . I have brought them in the kitchen for a wash out with a brush even.