On the heels of clarifying farmers’ right to repair their own equipment, EPA is escalating pressure on diesel engine manufacturers over ongoing Diesel Exhaust Fluid (DEF) system failures the administration claims continue to sideline farm machinery and trucks.
On Tuesday, EPA Administrator Lee Zeldin announced the agency is demanding detailed failure data from major diesel engine manufacturers as it considers additional rules aimed at reducing DEF-related shutdowns and derates that have plagued farmers, truckers and equipment operators for years.
The move builds directly on Monday’s EPA right-to-repair guidance announcement that clarified the Clean Air Act does not prohibit farmers from fixing their own non-road diesel equipment, which includes making temporary emissions overrides when necessary to complete repairs.
“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,” Zeldin said in a statement on Tuesday. “EPA understands this is a massive issue, which is why we have already established commonsense guidance for manufacturers to update DEF systems.
“Today, we are furthering that work and demanding detailed data to hold manufacturers accountable for the continued system failures,” he added.
While neither announcement fully rolls back DEF requirements on tractors, a step many farmers and truckers continue to push for, both signal movement in that direction.
With today’s news in the mix, here’s what farmers and truckers need to know:
1. Increased Operational Up-Time.
The most immediate benefit is the reduction of “forced downtime.” Under the clarified guidance announced on Feb. 2, farmers can now perform temporary emissions overrides to complete essential work, such as planting or harvesting, even if a DEF failure occurs. The extension of warning periods — specifically the 36-hour window for non-road equipment before a derate kicks in — provides a buffer to finish a job before seeking repairs.
2. Legal Empowerment for Repairs.
EPA has explicitly stated the Clean Air Act cannot be used by manufacturers as a shield to prevent farmers from fixing your own equipment. This clarification removes a major legal hurdle in the right-to-repair movement, potentially lowering repair costs by allowing farmers and independent mechanics to access the tools and software needed to address DEF-related faults.
3. Manufacturer Accountability.
Under Section 208(a) of the Clean Air Act, EPA is demanding warranty and failure data for Model Year 2016, 2019 and 2023 engines from 14 major on-road and non-road diesel manufacturers (covering 80% of the market). That shifts the burden of DEF reliability from the end-user to the manufacturer. EPA says the information will help determine whether persistent DEF problems are tied to specific product generations, system designs or materials, and will inform further regulatory steps in 2026. Manufacturers have 30 days to comply or face potential enforcement actions.
4. Impact on Machinery Values.
Auction data suggests farmers are already voting with their checkbooks. According to Machinery Pete, demand and values remain strongest for pre-DEF used equipment, while interest in DEF-equipped machinery has softened.
If these EPA actions lead to more reliable DEF systems or easier repairs, the high demand (and inflated prices) for older, less efficient equipment might eventually stabilize as newer models become less of a liability in the field.
5. More Changes are Coming.
When asked why EPA has not eliminated DEF requirements entirely,Zeldin said the agency said it is actively building on last summer’s guidance and actively moving toward “common-sense” adjustments that prioritize productivity alongside emissions standards.
EPA’s demand for warranty and failure data follows DEF guidance issued in August 2025 that significantly softened inducement rules. That guidance delayed severe derates, reduced sudden shutdowns and required manufacturers to update software so operators could continue safely working while addressing faults.
For heavy-duty trucks, warning periods were extended to up to 650 miles or 10 hours before derates begin, with weeks of normal operation allowed before speed is limited. Non-road equipment now sees no impact for the first 36 hours after a DEF fault.
EPA has also said that starting with Model Year 2027, new diesel trucks must be engineered to avoid sudden and severe power loss after running out of DEF.
