The U.S. Environmental Protection Agency (EPA) promised to take more action on behalf of truckers and farmers regarding Diesel Exhaust Fluid (DEF) system failures.
EPA Demands DEF Data From Diesel Engine Makers
On February 3, 2026, EPA Administrator Lee Zeldin announced that the agency is “demanding information from major diesel engine manufacturers on critical data from DEF system failures” as part of upcoming rulemaking to provide more relief for truckers and farmers.
The EPA has given manufacturers 30 days to provide 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 who fail to comply with the EPA’s request for information may face additional inquiries or penalties.
“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,” the agency said. “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.”
The EPA noted that “it is being thoroughly assessed whether derates may no longer be necessary for compliance.”
“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 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.”
New DEF Relief To Built On Previous EPA Action To Ease Loss Of Productivity From Derates
Zeldin said that the EPA plans to build on guidance issued in August 2025 which called on manufacturers to update system software in existing vehicles and equipment to prevent derates, or sudden speed and power losses caused by DEF systems.
According to the EPA, the August 2025 guidance resulted in significant relief from the loss of productivity:
“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.“
EPA also recently ruled that starting with Model Year 2027, all new diesel on-road trucks must be engineered to avoid sudden and severe power loss after running out of DEF.
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