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Recent EPA updates regarding diesel exhaust fluid (DEF) have raised questions across the fueling industry, but the bottom line for fuel site operators is clear: DEF is not going away.
Q: How do vehicles use DEF?
A: DEF is a high-purity urea solution used in diesel vehicles, including tractor-trailers and agricultural equipment, to convert nitrogen oxide (NOx) emissions into harmless nitrogen gas and water vapor before exiting the tailpipe. Under legacy rules, a vehicle’s engine control module would incrementally slow the vehicle’s speed capability — a process known as derating — if it detected DEF problems and they went unresolved. Problems commonly flagged included the DEF tank running out of fluid, hardware tampering and component failures.
Q: What DEF requirements is the EPA changing for vehicles?
A: In August 2025, the EPA significantly relaxed derate timelines, which gave drivers more time to address a DEF issue before the vehicle started derating. A guidance document issued in March 2026 allowed heavy-duty vehicle manufacturers to omit traditional urea concentration sensors, which were vulnerable to failures, and replace them with downstream NOx monitoring. A July 2026 proposed rule eliminates mandatory engine-power and vehicle-speed derates for newly manufactured heavy-duty highway engines starting in Model Year (MY) 2027 and no later than MY 2029. The MY 2027 proposed rulemaking is forward-looking, but the August 2025 and March 2026 guidance directly address in-use vehicles.
Q: How do the regulations impact the outlook for DEF?
A: DEF will remain inherent to diesel emissions compliance, but the purchasing patterns will likely change. Under the previous derate framework, drivers confronted with DEF issues would often make emergency stops purchasing boxed DEF to clear an active fault. Under the new framework that offers 10- to 160-hour grace periods, drivers will be able to align DEF replenishment with diesel fueling stops, shifting more of the DEF volume to high-speed DEF island dispensers.
Q: Have questions about DEF equipment? A: Source North America offers a wide assortment of DEF equipment. Contact your local Source representative to learn more. Additionally, consider checking out a new Rack to Retail podcast that discusses the proposed changes to DEF regulations.
