At Iowa State Fair, EPA Administrator Zeldin Announces Diesel Exhaust Fluid (DEF) Fix

EPA Issues Guidance to Address Derates, Power Loss Concerns Raised by American Farmers, Truckers, and Equipment Operators Without Compromising Environmental Standards

August 12, 2025

DES MOINES – Today, U.S. Environmental Protection Agency (EPA) Administrator Lee Zeldin announced new action to protect American farmers, truckers, and other diesel equipment operators from sudden speed and power losses caused by diesel exhaust fluid (DEF) systems. Alongside U.S. Small Business Administrator Kelly Loeffler at the Iowa State Fair, EPA issued clear guidance urging engine and equipment manufacturers to revise DEF system software in existing vehicles and equipment to prevent these sudden shutdowns, giving operators more time to repair faults without impacting productivity or safety. 

“We have heard loud and clear from small businesses across the United States that the current DEF system is unacceptable. It is unacceptable that farmers, truckers, construction workers, and many other small businesses continually experience failures of diesel-powered equipment when they need it most—costing millions of dollars in lost productivity,” said EPA Administrator Zeldin. “Today, we are responding to those concerns by calling on manufacturers to take action to update their software and eliminate the unnecessary sudden loss of power and frustrating shutdowns that too many Americans have experienced.” 

“The Trump Administration is fighting for farmers and truckers, as evidenced by the EPA’s new DEF guidance which is a big win for the millions of small businesses who rely on diesel engines - and who have been crushed by years of costly Green New Scam regulations,” said SBA Administrator Kelly Loeffler. “This change will save family farms an estimated $727 million per year and offers vital financial and operational certainty. I’m proud to work alongside EPA Administrator Lee Zeldin to reduce red tape for our nation’s producers and deliver real relief for hardworking Americans."

“This is yet another example of President Trump’s cabinet working hand in hand to cut absurd and wasteful government regulations that tie the hands of our farmers, ranchers, and small business owners,” said Secretary of Agriculture Brooke L. Rollins. This common sense reform will allow our agricultural producers to spend more time in the fields than in the repair shop. On behalf of farmers and ranchers across America, I want to thank Administrator Zeldin for taking this historic action today. This is on top of the Trump Administration’s actions to support biofuels more than any other administration in the history of our country, putting our corn and soybean farmers first.” 

“No farmer should ever have their tractor literally brought to a halt in the middle of a field because of a Green New Deal style regulation from Washington,” said Senator Joni Ernst (R-IA). “The previous arbitrary diesel exhaust fluid system guidelines severely hurt farmers, truckers, and small businesses that rely on diesel powered trucks. Not only will the new guidelines save family-run farms hundreds of millions every year, but it is also simply common sense.”

Starting with model year 2027, EPA requirements state that all new diesel on-road trucks must be engineered to avoid sudden and severe power loss after running out of DEF. To fix the problem for vehicles already in use, EPA’s new guidance, developed in collaboration with manufacturers, will work to ensure that the necessary software changes can be made on the existing fleet. In addition to providing certainty to manufacturers about how EPA wants this issue resolved, the agency is not requiring separate approvals beyond that provided in EPA’s guidance. This ensures that bureaucratic steps do not delay manufacturers’ ability to put solutions into the field. 

EPA remains committed to protecting air quality and public health while ensuring that engine operators can depend on the equipment they need. EPA will continue to work with all stakeholders to ensure practical, durable solutions that simultaneously support emissions reductions and reliable operations.

Please see EPA's Diesel Exhaust Fluid website for more information.

Background

When DEF runs out or a system sensor fails, current systems can force a vehicle to drastically reduce speed or become inoperable. In many cases, vehicles are limited to as little as five miles per hour within hours of a DEF-related fault, causing significant disruptions in logistics, agriculture, and construction. Although this derate strategy was intended to ensure compliance with EPA’s Tier 4 Emissions Standards, it has caused needless frustration, operational delays, and real economic hardship for countless farmers, truckers, and equipment operators.

Since 2010, most on-road diesel trucks and many types of nonroad equipment (such as tractors and construction machinery) have used selective catalytic reduction (SCR) systems that inject DEF into exhaust streams to reduce nitrogen oxide (NOx) emissions.

Motor Coaches

HD Trucks

HD Pickups and LD Cars

Nonroad