DEF - all the same?

DEF is mandated by the Feds, and the specification is pretty specific. Urea is one of the cheapest chemicals available, and the only other ingredient is the distilled water in which it is dissolved. Pretty simple to make, pretty simple to test and pretty hard to screw up without bringing the Feds around to investigate. About the only two things that can go wrong is that it can be degraded by being too old and the clown adding it to the tank can get grease, dirt, or other contaminants in there. Other than that, pretty foolproof. Unlike the REST of the emissions system.

So, all DEF is supposed to be the same. Buy whatever you can find when you need it, and don't plan to store it for years in your trunk or garage. Fresh is the word.