I was told a little compressed air is used to inject the DEF, and moisture in your air tanks can promote DEF crystalization. Yes or no?Def is injected into the decomposition Tube where it passes thru a mixer plate and into the SCR Catalyst. This all happens down stream from the DPF, initially if you have a Freightliner product there is a def quality sensor in the Def Tank on 2013 and newer models and the wiring to it is common to corrode. Also the inlet and out let Nox sensors take readings and can throw this code in a truck without the quality sensor and that can be caused by the list of other problems I gave, not necessarily buying bad def but, it can be contaminated by other things. There is a metal coolant tube that runs through the tank to keep the def fluid in winter. They are prone to cracking. Leaking def injector causing def to crystallize on the mixer plate is the third most common.