What is it with DEF?
Just what is the Diesel Exhaust Fluid (DEF) ? What does it do and why do I need it? This is my first diesel and I never heard of it.
Forum Discussion
You'll find out if your truck needs it when you run out; your truck won't go. My message center gives me plenty of advance warning. 500 miles for first message. I get 5000 - 7000 miles between fills depending on how much towing is involved.
