[Javi]

Although my "RULES" were tongue in cheek, it is important to check the DEF level for your truck whether you have a gauge or have to push a button to check.

DEF usage is dependent on many things including axle ratio, type of driving and even driving styles. My experience with DEF has been limited to my '12 F250 and now my '15 F350. The F250 had a 3:31 rear end and even towing I didn't need to fill the DEF very often; usually getting around 2000 miles before seeing the "LESS THAN 1/2" warning. My new F350 has a 3:73 and so far it looks like I'm going to see the warning a little more frequently; maybe 1200 to 1500 miles.

From what I have found by research it is important to let the tank reach the "LESS THAN 1/2" warning before topping off as the "brain" doesn't deal with constantly full very well. It seems that eventually it will decide that you aren't using DEF at all if the level doesn't trigger one of the sensors..
This really doesn't seem plausible but stranger things can happen. That shouldn't be a problem because even after receiving the initial warning you have at least a 1000 miles before running out.

I simply have added checking the level with the button to my startup routine. After starting the motor and while I'm giving the motor a minute to wake up before putting the truck into gear.. takes all of 15 seconds, then I hook up the seat belt and head out.. If I see the warning I buy a jug or fill the tank at the next fuel stop..