Last year, the Environmental Protection Agency made moves to clean up problems with diesel exhaust fluid or DEF systems. Less than a year later, Daimler Truck North America is doing its part to ease DEF headaches.
Since Donald Trump returned to the White House, the EPA has made efforts to roll back emission policies that go as far back as 15 years ago. Part of those efforts includes going after emissions mitigation that truck drivers have complained about for years: DEF.
In addition to claims that DEF has reduced engine quality, truck drivers are also subject to quick engine deratings if sensors identify DEF issues. That could leave drivers stranded before they can fix the problem.
Recognizing the problems with DEF, the EPA issued new guidance for engine and truck manufacturers last August. That guidance urged manufacturers to update their system software to prevent sudden shutdowns.
Until recently, many engines would rapidly derate to 5 mph within four hours. It was not uncommon for a sensor failure to unnecessarily derate an engine.
Under new guidance, engines would be derated gradually over a longer period, giving drivers more time to address the issue. Rather than being limited to 5 mph within a few hours, drivers would have at least 650 miles or 10 hours before a 15% torque reduction kicked in. Drivers would have nearly a week or 8,400 miles before the truck would be limited to 25 mph.
Source: U.S. Environmental Protection Agency
Freightliner and Western Star owners may have noticed those changes.
Daimler Truck North America recently announced that it is equipping trucks with updated DEF software consistent with the EPA’s August 2025 guidance.
According to Daimler, the final speed limit has increased from 5 mph to 25 mph. The time it takes to reach final inducement has been “extended.”
New trucks with Detroit engines are being shipped with updated DEF software, often referred to by manufacturers as DEF “inducement” software. Daimler has been updating software on more than 300,000 trucks already out on the roads since February. That includes model years 2021-25 DD15 engines and 2022-25 DD13 engines. Updates will continue throughout the year.
“For too long, small businesses like farmers, truckers, and construction workers have borne the cost of unreliable DEF systems through expensive repairs and needless downtime,” U.S. Small Business Administration Administrator Kelly Loeffler said in a statement. “This is why the SBA has been calling on OEMs to implement recent EPA guidance. The SBA welcomes Daimler Truck North America’s decision to equip vehicles with updated DEF inducement software, a common-sense step that gives operators greater reliability while reducing costs. This is exactly the kind of relief that the hardest working Americans deserve.”
More DEF relief ahead?
New inducement schedules may be just the beginning for drivers wanting more improvements to DEF systems.
One of the issues with DEF systems is sensor false alarms. Drivers might find the derating or inducement schedule kicking in despite no DEF issues.
In March, the EPA issued more guidance to manufacturers dealing with DEF sensors. Specifically, the agency is allowing manufacturers to use sensors that have fewer false alarms but weaker detection elsewhere.
About a month prior, the EPA demanded information on emissions-related components from the top 14 manufacturers. At the time, EPA Administrator Lee Zeldin posted on social media that the agency hoped “to PERMANENTLY eliminate the deratements ENTIRELY.”
In January, the Department of Justice announced it would no longer pursue criminal charges against anyone tampering with onboard diagnostic devices. However, the department and the EPA will still pursue civil enforcement “when appropriate.” LL
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