EPA Issues New Diesel Exhaust Fluid Guidance

DES MOINES, IA — The U.S. Environmental Protection Agency announced new guidance aimed at preventing sudden speed and power losses in diesel-powered vehicles and equipment, a move intended to protect farmers, truckers and other operators from costly disruptions.

EPA Administrator Lee Zeldin unveiled the update Aug. 12 at the Iowa State Fair alongside U.S. Small Business Administrator Kelly Loeffler. The guidance directs engine and equipment manufacturers to revise diesel exhaust fluid (DEF) system software to allow more time for repairs before shutdowns occur, without compromising emissions standards.

“We have heard loud and clear from small businesses across the United States that the current DEF system is unacceptable,” Zeldin said. “Today, we are responding to those concerns by calling on manufacturers to update their software and eliminate unnecessary shutdowns.”

The new rules, effective for model year 2027 vehicles, require manufacturers to engineer trucks to avoid sudden and severe power loss when DEF runs out. EPA’s updated approach allows necessary software changes to be made on existing equipment without separate approvals.

Texas Agriculture Commissioner Sid Miller praised the change, calling it “proof that, under President Trump, Washington is finally listening to rural America.” Miller said the measure will save farmers and small businesses an estimated $727 million annually in lost productivity, repairs, missed deadlines and penalties.

“For years, I’ve heard from Texas farmers, ranchers, and truckers forced off the job by ridiculous DEF shutdowns right in the middle of planting, harvest, or hauling,” Commissioner Miller said. “This nonsense has robbed our producers of time, money, and peace of mind. 

Current DEF shutdown rules, designed to meet EPA’s Tier 4 emissions standards, can slow vehicles to as little as 5 mph within hours of a DEF fault, causing delays in agriculture, construction and logistics. The revised guidelines extend repair windows across multiple vehicle categories, including motor coaches, heavy-duty trucks, pickups, cars and nonroad equipment.

“Texas agriculture runs on hard work and diesel power,” Miller said. “This action cuts Washington out of the driver’s seat, strengthens our rural economy, and delivers the relief farmers and ranchers have been demanding for years. This new EPA guidance will save producers millions, stop costly equipment shutdowns, and keep Texas agriculture plowing ahead.”

EPA said it will continue working with stakeholders to ensure reliable operations while maintaining emissions reductions.

Full guidance details are available on the agency’s Diesel Exhaust Fluid website.