[DmaxDually]

Now I'm curious about the operation of the DEF system. Maybe that's why they are having so many DEF issues. I don't know the freeze point of DEF fluid but If you fill your DEF tank (5+ gals) then it freezes into a solid block of ice over night it can't be good for the components (sensors) in the tank. As we all know when liquid freezes it expands and needs some place to go. If your tank is full the ice can be breaking or damaging these sensors as it expands. I don't know how long it would take or if the tank heater can even defrost a 5 gal solid block of ice sitting outside in sub zero temps.