The cuts to DEF derivatives are the latest move by the Trump administration to roll back Biden-era emissions rules. (Ebliss/Getty Images)
key takeaways:
- The EPA is proposing to eliminate DEF-related engine derailments and replace them with dashboard alerts, a move aimed at reducing downtime and keeping trucks running.
- The change is part of a broader effort by the Trump administration to modify Biden-era NOx rules while reducing cost and reliability concerns for fleets and manufacturers.
- While carriers and the ATA largely welcomed the proposal, fuel marketers and truck-stop groups warned it could undermine a technology they see as a major emissions-success story.
The Environmental Protection Agency has proposed eliminating engine derating related to diesel exhaust fluid, replacing sequential dialing of truck displays with visual or audible notifications.
A surprise inclusion in the long-awaited notice of proposed rulemaking (NPRM) on changes to nitrogen oxide tailpipe emissions rules, eliminating the DEF derivative is the latest step in the Trump administration’s ongoing rollback of Biden-era emissions rules.
It saw the largest protest ever from the trucking industry, with trucks stopping, fuel marketers and environmental lobbyists questioning the speed 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 Fuels Marketers.
Fialkov said, “While the Administration’s impatience is understandable, we believe it is counterproductive to prematurely interrupt (earlier bait-related actions) when allowing it to proceed would obviate the need for today’s DEF-related actions.”
But other trucking industry supporters were more complimentary.
Today, the Trump EPA proposed eliminating DEF derivatives entirely as part of a common-sense amendment to the previous administration’s heavy-duty NOx rule.
This proposal builds on EPA’s ongoing efforts to help address DEF system failures – from reversing unnecessary diversions to… pic.twitter.com/EQALjdeFQR
– US EPA (@EPA) 9 July 2026
Patrick Kelly, vice president of energy and environmental affairs for the American Trucking Associations, told Transportation Topics: “ATA appreciates EPA’s efforts to evaluate regulations that impact the operating efficiency of commercial vehicles.”
DEF systems have played an important role in reducing emissions from modern diesel engines, Kelly said, but trucks can also be stranded due to engine failure due to emissions system issues.
“As EPA considers potential changes, ATA encourages a balanced approach that preserves environmental progress while improving equipment reliability and ensuring the fleet can continue to deliver the nation’s freight safely and efficiently,” he said.
EPA intends to provide carriers and farmers with greater flexibility and uptime and follow revised guidance on DEF inspiration parameters announced in August 2025 that will increase the minimum speed for trucks before refilling DEF tanks or repairing sensors.
The proposal also builds on EPA’s July 1 guidance directing truck and engine manufacturers to offer customers the opportunity to repair DEF and other on-highway vehicle environmental control systems.
Hearty welcome from ATD, ATA
The July 1 guidance received a more similar response from the trucking industry, including U.S. truck dealers.
“ATD/NADA commends the President and EPA for improving the certification process for vehicle emissions parts without disrupting the 2014 and 2015 auto and truck MOUs, which continue to ensure a competitive vehicle repair market,” said Amy Wright, spokeswoman for ATD and the National Automobile Dealers Association.
ATA’s Kelly said: “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 running.”
The July 1 guidance was expected following the February EPA guidance; 9th July is less.
Before the waiver was proposed on July 9, truckmakers were in the process of responding to the August 2025 guidance.
OEMs release software updates
Earlier in July, Packer and Cummins began releasing software updates that included revised DEF inspiration parameters in accordance with the August 2025 guidance.
Under the revised guidance, the speed limit at the final spur will be increased from 5 mph to 25 mph, and the time to reach the final spur for component-related issues will be extended.
Packer and Cummins followed Daimler Trucks North America in releasing the software update.
Cummins is offering updates for more than 1.5 million engines in medium and heavy duty trucks, including some model year 2017 trucks, the company said July 6.
Packer, the parent company of Kenworth and Peterbilt, will introduce updated software for vehicles equipped with MX-11 and MX-13 engines, the company said July 6.
DTNA said on June 22 that it began rolling out the update in February to approximately 330,000 in-service vehicles with DD15 engines (model years 2021-2025) and DD13 engines (model years 2022-2025).
defining technology
Selective catalytic reduction technology uses DEF to convert nitrogen oxides into nitrogen and water, supporting compliance with EPA emissions standards.
There are built-in safeguards on induction trucks and tractors that ensure that the emissions system works properly by cutting down on vehicle speed and power should problems be detected.
The SCR technology and hence the DEF requirement was introduced to meet the 2010 model-year EPA mandate. DEF is a non-toxic, colorless and odorless solution consisting of 32.5% urea and 67.5% deionized water.
Engines will still need DEF. The deceleration prompts the driver to correct the problem, usually refilling the DEF tank, repairing a faulty sensor or component, or performing a regeneration cycle.
But in March, the EPA approved a guidance update that allows truck makers to replace urea-quality sensors with nitrogen oxide sensors.
