I don't really want to believe any of the possible scenarios. We are still out of town, so I haven't seen the diesel fuel in it for my own eyes. I don't know if these vans come from the factory full of DEF or if the dealerships do it. But, if there is diesel fuel in the def tank, it came from the dealership or the dispenser of DEF when I filled it awhile back. I know, both scenarios seem unlikely.