Expert guides, tips and insights for diesel exhaust fluid maintenance

DEF Academy

Aerial view of Chicago intermodal rail yard with shipping containers and semi trucks - DEF additive midwest
DEF Academy

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.

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Mercedes Sprinter DEF filler cap close-up
DEF Academy

Diesel DEF: The Complete Guide to Diesel Exhaust Fluid (Specs, Costs, Maintenance & Failure Modes)

Diesel exhaust fluid is a 32.5% urea / 67.5% deionized water solution to ISO 22241, required on every Tier 4 Final diesel sold in the U.S. since 2010 on-highway and 2014 off-highway. This guide covers DEF chemistry and EPA history, which engines need it, real consumption rates and costs from pump to bulk tote, shelf life and storage, the failure modes that kill SCR systems (crystallization, contamination, freezing, dosing faults), the trouble codes you’ll see, maintenance habits that prevent shop bills, and the myths that cost operators money.

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