That is what I thought until some people in other forums said that they got a CEL with a code for poor quality DEF . It could be due
to excess heat which would make some of the deionized water to evap and raise the % of urea too high, then if temps get too low
crystalization could cause problems.
that's what caused my DEF error. This was from factory as well. Tech tested % and said it was above allowance. Drained tank, refilled. No errors yet after about 500 miles