EPA doubles down on DEF overhaul, demands data from manufacturers

The Environmental Protection Agency continues its crusade to roll back truck emission regulations. The latest move is a doubling down in its efforts to reform diesel exhaust fluid (DEF) rules.

For years, truck drivers and farmers have complained about newer diesel engines that require DEF systems. In addition to sudden shutdowns, drivers have reported reduced engine lifespan and performance.

During an EPA public hearing in 2022, Owner-Operator Independent Drivers Association Executive Vice President Lewie Pugh warned the agency about issues with emission systems.

“My 2012 truck with all the latest EPA-compliant technology was in the shop for repairs more than the other four trucks I owned prior to this one combined,” Pugh said in his testimony. “In a period of 250,000 miles, or two and a half years, I had to have the entire DPF system completely replaced at a cost of $6,000 each time.”

Last August, the EPA announced new guidance for engine and truck manufacturers. The agency urged them to update the DEF system software on current vehicles.to prevent sudden shutdowns.

That guidance applies only to model year 2026 and older trucks. DEF systems for model year 2027 and newer trucks are regulated under a separate heavy-duty NOx rule passed in 2022. New rules tighten enforcement and make it harder to cheat the system.

The EPA is targeting the latest DEF rules and is fighting fire with fire.

DEF systems are required in newer diesel engines after the EPA strengthened emission standards under the Clean Air Act. Ironically, the Trump administration is using the Clean Air Act to undermine the technology.

Section 208(a) requires manufacturers to submit information on emissions-related components to determine whether failures are due to specific products. EPA is demanding that info from the top 14 manufacturers that account for more than 80% of all products used in DEF systems. Manufacturers have 30 days to comply.

What does the EPA plan on doing with information? Simply put, the agency is setting the stage to withdraw the 2022 heavy-duty engine and vehicle NOx rule. While that may not get rid of DEF, it could eliminate derating requirements “permanently” and “entirely,” EPA Administrator Lee Zeldin said.

As I traveled throughout all 50 states during my first year as EPA Administrator, I repeatedly heard disaster stories of Diesel Exhaust Fluid (DEF) system failures and absurd deratements. That’s why, in August 2025, I reversed the deratements through an updated guidance document…

— Lee Zeldin (@epaleezeldin) February 3, 2026

This is just the latest action the federal government has taken against DEF and other truck emission rules.

The day before the latest announcement, the EPA issued guidance giving people the right to repair farm and other nonroad diesel equipment. This allows farmers to repair broken DEF systems at home or on the field, rather than requiring a trip to a certified repair shop.

In January, the Department of Justice announced it will no longer seek criminal charges in tampering cases. Civil penalties and fines still apply.

Just last week, the EPA finalized a rule disapproving of California’s Clean Truck Check requirements for out-of-state trucks. However, the California Air Resources Board dismissed the rule, asserting that the EPA lacks authority over the program. It is not clear how Clean Truck Check enforcement will proceed.

OOIDA applauded EPA’s recent moves.

“On the heels of EPA’s Final Rule last week restricting CARB’s authority on trucks registered outside of California, OOIDA applauds the agency’s willingness to give truckers more flexibility when dealing with faulty emissions systems,” OOIDA President Todd Spencer said. “We believe the forthcoming data from engine manufacturers will once again prove that problems with nonsensical DEF regulations have sidelined small-business truckers for too long. We look forward to continued engagement with Administrator Zeldin and his staff to implement additional emissions solutions that better reflect the realities of trucking.” LL