EMA
In a significant development for the diesel industry, the U.S. Environmental Protection Agency (EPA), led by Administrator Lee Zeldin, has issued a directive requiring major diesel engine manufacturers to provide comprehensive data on Diesel Exhaust Fluid (DEF) system failures. Announced on February 3, 2026, this initiative gives manufacturers just 30 days to comply, with a focus on addressing persistent issues that have plagued truckers, farmers, and other operators of diesel-powered equipment.
The EPA's request targets data from key model years—2016, 2019, and 2023—including failure rates, repair details, and warranty claims. The goal is to independently evaluate whether these problems stem from specific designs or product generations. Common complaints include sudden engine derates, loss of speed, and complete shutdowns, which not only disrupt productivity but also raise serious safety concerns on the road and in the field. Non-compliance with this data submission could lead to substantial penalties under the Clean Air Act.
This action builds on the EPA's August 2025 guidance, which urged manufacturers to implement software updates for existing fleets. These updates aim to mitigate severe derates by providing extended warnings—such as 650 miles or 10 hours for initial faults, followed by milder restrictions for up to 4,200 miles. For nonroad equipment, like agricultural machinery, the guidance permits up to 36 hours of operation before any torque reduction. Looking forward, model year 2027 on-road trucks will be required to eliminate sudden power losses entirely when DEF levels are low.
Additionally, a clarification issued on February 2, 2026, reinforces farmers' rights to repair nonroad diesel equipment, including DEF systems, without risking warranty invalidation under the Clean Air Act. DEF systems, introduced in 2010 to support selective catalytic reduction (SCR) technology and meet stringent NOx emission standards, have faced ongoing criticism due to sensor malfunctions, crystallization problems, and overly aggressive inducement strategies that can leave vehicles stranded.
By compelling the top 14 manufacturers—who represent over 80 percent of the market—to submit detailed data, the EPA is positioning itself to drive improvements in system designs and materials. This could translate to fewer breakdowns, reduced repair costs, and more efficient fuel utilization, ultimately stabilizing diesel demand in critical sectors like transportation and agriculture.
Fewer disruptions mean more consistent operations for end-users, supporting steady diesel consumption and distribution. The collected data will also inform upcoming 2026 rulemaking, potentially leading to revisions or withdrawals of elements from the 2022 heavy-duty NOx rule. Such changes could prioritize practical solutions that maintain emissions compliance without unnecessary operational penalties.
