Def freezes, and there is supposedly a heater in the tank. Does anybody know what happens til the def starts to flow? Is the PCM or ECM programmed to ignore the fact that there is no flow? How does the fluid in the line get thawed out? Hopefully the heater has enough capacity to overcome the windchill!

 

from what I was told it will start to freeze at 12deg and it wont affect anything because the heater will have time to thaw it out way before you start producing NOX.

 

The DEF usage is directly tied to high EGT. You will not use any at startup. If you are running at -35f the computer knows ambient temperature and waits until the DEF has liquified.