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EPA proposes end to DEF derates to mixed reception
Drivers to receive visual or audible notifications instead
Cutting DEF derates is the latest step in the Trump administration’s rollback of Biden-era emissions regulations. (Eblis/Getty Images)
Key Takeaways:
- EPA is proposing to eliminate DEF-related engine derates and replace them with dashboard alerts, a move aimed at reducing downtime and keeping trucks operating.
- The change is part of the Trump administration’s broader effort to revise Biden-era NOx regulations while easing costs and reliability concerns for fleets and manufacturers.
- While carriers and ATA largely welcomed the proposal, fuel marketers and truck-stop groups warned it could undermine a technology they view as a major emissions-success story.
The Environmental Protection Agency has proposed ending diesel exhaust fluid-related engine derates, replacing the gradual dialing back of truck performance with visual or audible notifications.
A surprise inclusion in a long-awaited notice of proposed rulemaking (NPRM) on changes to nitrogen oxide tailpipe emissions regulations, axing DEF derates is the latest step in the Trump administration’s ongoing rollback of Biden-era emissions regulations.
It also saw the greatest pushback yet from the trucking industry, with truck stops, fuel marketers and environmental lobbyists questioning the pace of introduction and impact on DEF markets.
“The widespread adoption of DEF technology represents perhaps the most significant environmental success story for liquid fuels in the trucking sector,” said David Fialkov, head of government affairs for Natso and Sigma: America’s Leading Fuel Marketers.
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“While the administration’s impatience is understandable, we believe it is counterproductive to prematurely disrupt [earlier inducement-related actions] when allowing it to proceed would negate the need for today’s DEF-related actions,” Fialkov added.
But other trucking industry advocates were more complimentary.
American Trucking Associations Vice President of Energy and Environmental Affairs Patrick Kelly told Transport Topics: “ATA appreciates EPA’s efforts to evaluate regulations that affect the operational efficiency of commercial vehicles.”
DEF systems have played an important role in reducing emissions from modern diesel engines, but engine derates triggered by emissions system issues can also leave trucks stranded, Kelly said.
“As EPA considers potential changes, ATA encourages a balanced approach that preserves environmental progress while improving equipment reliability and ensuring fleets can continue delivering the nation’s freight safely and efficiently,” he added.
EPA’s intention is to offer carriers and farmers greater flexibility and uptime and follows revised guidance on DEF inducement parameters announced in August 2025 that would lift the minimum speed for trucks before DEF tanks must be refilled or sensors repaired.
The proposal also builds on July 1 guidance from EPA instructing truck and engine manufacturers to offer customers the opportunity to repair DEF and other on-highway vehicle environmental control systems.
Warm receptions from ATD, ATA
The July 1 guidance found a more homogenous response from the trucking industry, including from American Truck Dealers.
“ATD/NADA applauds the president and the EPA for reforming the certification process for vehicle emissions parts without disrupting the 2014 and 2015 auto and truck memorandums of understanding that continue to ensure a competitive vehicle repair marketplace,” said Amy Wright, ATD and National Automobile Dealers Association spokeswoman.
ATA’s Kelly added: “ATA welcomes efforts to give motor carriers greater flexibility to maintain and repair their equipment. Timely access to qualified repair options can help reduce costly downtime and keep trucks moving.”
The July 1 guidance was expected, following February EPA guidance; the July 9 less so.
Before the July 9 proposal to ax deratements, truck manufacturers were in the process of responding to the August 2025 guidance.
OEMs roll out software updates
Earlier in July, Paccar and Cummins began rolling out software updates that incorporated the revised DEF inducement parameters according to the August 2025 guidance.
Under the revised guidance, the speed limit in final inducement will be increased to 25 mph from 5 mph, and the time to reach final inducement for component-related issues will be extended.
Paccar and Cummins followed Daimler Truck North America in rolling out software updates.
Cummins is offering updates for more than 1.5 million engines in medium- and heavy-duty trucks, including certain trucks dating to model year 2017, the company said July 6.
Kenworth and Peterbilt parent Paccar will offer updated software for vehicles equipped with MX-11 and MX-13 engines, the company said July 6.
DTNA said June 22 it began rolling out the update in February for about 330,000 in-service vehicles with DD15 engines (model years 2021-2025) and DD13 engines (model years 2022-2025).
Defining the technology
Selective catalytic reduction technology uses DEF to convert nitrogen oxides into nitrogen and water, supporting compliance with EPA emissions standards.
Inducements are the built-in safeguards on trucks and tractors that ensure emissions systems function appropriately by cutting vehicle speed and power should issues be detected.
SCR technology and therefore the need for DEF was introduced to meet 2010 model-year EPA mandates. DEF is a nontoxic, colorless and odorless solution comprising 32.5% urea and 67.5% deionized water.
Engines will still require DEF. The slowdown “induces” the driver to correct the issue, typically by refilling the DEF tank, repairing a faulty sensor or component, or performing a regeneration cycle.
But in March, EPA approved a guidance update that allows truck manufacturers to replace urea-quality sensors with nitrogen oxide sensors.
