
Diesel DEF FAQ: Every Question Answered About Diesel Exhaust Fluid
Diesel Exhaust Fluid (DEF) is required on every diesel engine built in North America after 2010. It’s an aqueous urea solution — 32.5% high-purity urea, 67.5% deionized water, conforming to ISO 22241-1 — injected into the exhaust to neutralize NOx emissions. This FAQ answers the 25 most-searched questions about DEF, from “what is it” through “why is my truck in limp mode.” For comprehensive coverage, see our Diesel DEF Complete Guide. NüDef solves DEF’s biggest field problem: crystallization in storage and in your SCR system.




























