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

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

February 3, 2026

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 guidancein 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.

Background

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

Prior to EPA's August guidance, when DEF ran out or there was an unexpected mechanical failure, systems forced a vehicle to drastically reduce speed or become inoperable. In many cases, vehicles were limited to as little as five miles per hour within hours of a DEF-related fault. This caused needless frustration, operational delays, and real economic hardship for operators. Under the Trump EPA's August guidance, major changes were undertaken. Heavy-duty trucks now should only receive a warning light for 650 miles or 10 hours after a fault is detected. Following that time, the engine will only mildly derate, allowing trucks to operate normally and without speed limits for up to 4,200 miles or two work weeks. Only after about four work weeks does speed drop to 25 mph until repairs are made. Nonroad equipment has no impacts for the first 36 hours before a slight torque reduction then takes effect.

In addition to EPA's August 2025 guidance, EPA stated that starting with MY 2027, all new diesel on-road trucks must be engineered to avoid sudden and severe power loss after running out of DEF.

Yesterday, EPA issuedguidance to manufacturers, making it abundantly clear that under the Clean Air Act, Americans have the right to repair their farm and other nonroad diesel equipment. This guidance will allow farmers to fix broken DEF systems at home or in the fields, saving them time and money, while the agency continues its work on DEF.