How to fill up

Diesel exhaust fluid is a liquid used to reduce the amount of air pollution created by a diesel engine. Specifically, DEF is an aqueous urea solution made with 32.5% urea and 67.5% deionized water.
Like any other engine fluid, diesel exhaust fluid (DEF) is essential to keeping your vehicle up and running.
DEF became commonplace on diesel vehicles starting in 2010 to comply with tightening emissions standards.
Like diesel fuel, your vehicle consumes DEF as you drive, albeit at a much slower rate. Strict emissions regulations force vehicle manufacturers to reduce engine performance or prevent starting altogether when DEF runs out. Your vehicle will give you ample warning as your DEF level starts to get low, and some cars and trucks even incorporate a DEF gauge in the dash.
When you run low, your vehicle may enter a reduced power mode meant to conserve the DEF you have left. If you do happen to run out of DEF entirely, you will be unable to start your car until you refill the tank.