Another regulatory win for the industry.

Administrator Zeldin Takes Additional Measures to Address Diesel Exhaust Fluid (DEF) Issues for American Farmers and Truckers



February 3, 2026

Contact Information
EPA Press Office ([email protected])
WASHINGTON – Today, U.S. Environmental Protection Agency (EPA) Administrator Lee Zeldin took another step to further the Trump EPA’s work to address widespread concerns from farmers, truckers, motor coach operators, and other diesel equipment operators regarding Diesel Exhaust Fluid (DEF) system failures. As a follow up to new guidance in August 2025 reversing deratements that were harming farmers and truckers, EPA is pursuing rulemaking opportunities to provide further relief for Americans. To strengthen the agency’s ongoing efforts, EPA is demanding information from major diesel engine manufacturers on critical data from DEF system failures. The data collected will allow EPA to independently evaluate ongoing system failures and help inform next steps the agency takes in 2026 pertaining to DEF.

“As I traveled to all 50 states during my first year as EPA Administrator, I heard from truck drivers, farmers, and many others rightly complaining about DEF and pleading for a fix. EPA understands this is a massive issue, which is why we have already established commonsense guidance for manufacturers to update DEF systems,” said EPA Administrator Zeldin. “Today, we are furthering that work and demanding detailed data to hold manufacturers accountable for the continued system failures. The Trump EPA is committed to ending unnecessary frustrations and days lost on the road and in the field for American farmers and truckers.”

The issue facing farmers, truck drivers, and equipment operators remains clear to the agency. Sudden speed losses and shutdowns caused by DEF system failures compromise safety and productivity. The Trump EPA’s guidance, which significantly reversed deratements, called on manufacturers to revise DEF system software in existing fleets to prevent these sudden shutdowns and give operators more time to repair faults. EPA recognizes that to improve systems, the product designs and materials for these systems must also be the highest quality possible. With today’s action, EPA is taking another step to address any potential insufficiencies with system parts to better advance future rulemaking and reduce system failures.

Under Section 208(a) of the Clean Air Act, EPA is authorized to require manufacturers to provide information needed to assess whether emission control systems are functioning properly and whether manufacturers are meeting their obligations to identify and fix defects. EPA is demanding information from the top 14 on-road and nonroad manufacturers that account for over 80 percent of all products used in DEF systems. Specifically, EPA is requiring data on warranty claims, failure rates, and repair information for Model Years (MY) 2016, 2019 and 2023 emission control products to determine whether ongoing DEF system failures are related to a specific generation of products. Manufacturers will have 30 days to provide the requested information; failure may result in additional inquiries or penalties.

The agency is committed to working with manufacturers to ensure practical, durable solutions that simultaneously support emissions reductions and reliable operations. EPA has been meeting with manufacturers to receive updates on their progress in developing improved software in response to EPA’s guidance. The agency has consistently encouraged manufacturers to provide the relief as quickly as possible.

EPA is actively working on its proposal for the reconsideration of the 2022 Heavy-Duty Engine and Vehicle NOx rule. It is being thoroughly assessed whether derates may no longer be necessary for compliance. EPA is committed to keeping the protection of air quality and human health at the forefront of every action the agency takes.
Administrator Zeldin Takes Additional Measures to Address Diesel Exhaust Fluid (DEF) Issues for American Farmers and Truckers | US EPA