[SaVAGeSoot]

There's no mystery about it. It's spelled out in the warranty summary that no owner reads.

AdBlue® (diesel exhaust fluid) usage may increase, and, as a result, require more frequent refilling of your AdBlue® tank. As a courtesy to you, your vehicle will be returned to you with a full tank of AdBlue® and fuel during the Approved Emission Modification (AEM).
AdBlue® refillings will also be offered free of charge between service intervals for:
 10 years or 120,000 miles, whichever occurs first from the vehicle’s original in-service date;
OR
 4 years or 48,000 miles, whichever occurs first, from the date and mileage of the emissions modification

 

[JoshC]

I will say when you go to the dealer they will try to slime out of it, theyve tried to charge me and say it only pertains to in between oil changes. Quick argument and they usually remove the charge. I've used peak def probably 3 times, ended up with free ones from work and never had an issue until recently and it didn't even turn out to be the def but a nox sensor failing. Couple times I've used vw def and didn't have an issue at all but it's hard to quantify.