After purchasing the truck, before leaving the dealership, I noticed the DEF wasn't showing full. The salesman filled it and it overflowed, but it still didn't show full. I filled it multiple times, but still never showed full. Then one day, after driving on bumpy roads, it just started working. However, I have not filled it completely yet, recently. This is a serious issue because if you run out of DEF, the truck will go into limp mode and could leave you stranded.