Thanks any thoughts on why the low DEF warning is only showing in the app and not the truck itself? Current DEF gauge has all but 1 bar currently in the def level screen.There is a TSB for DEF level errors on GM trucks and SUVs. I think the TSB is 22-NA-150 (it's been updated to add new model years several times). It's a software update.
The level sensors in the DEF tank work the same way water & waste tank levels are in an RV (not very accurate). You can't have a float since the DEF is allowed to freeze in the tank.