The Environmental Protection Agency on Tuesday announced sweeping changes to rules governing diesel exhaust fluid (DEF) systems, aimed at preventing sudden power losses that have long frustrated farmers, truckers and bus operators.
The Trump administration says the guidance, which takes effect immediately, will ease operational disruptions and reduce safety risks while maintaining emissions standards.
EPA Administrator Lee Zeldin unveiled the changes during a press call from the Iowa State Fair alongside Small Business Administrator Kelly Loeffler, Agriculture Secretary Brooke Rollins and Sen. Joni Ernst, R-Iowa.
“The United Motorcoach Association applauds the new guidance from the Environmental Protection Agency (EPA) under the leadership of Administrator Lee Zeldin regarding Diesel Exhaust Fluid regulations for motorcoaches,” remarked UMA’s President and CEO Scott Michael. “EPA’s new guidance will improve safety, avoid passengers stranded on the side of the road, and unnecessary towing costs while maintaining the goal of safeguarding the environment.”
The policy allows manufacturers to reprogram existing vehicles to avoid abrupt “derates” — a rapid reduction in engine power — that can cut a vehicle’s speed to as little as 5 mph within hours of a DEF system fault.
“This is yet another common-sense policy,” Zeldin said. “We can protect the environment and grow the economy at the same time.”
Under current rules, a sensor failure in a DEF system can trigger severe speed limits within four hours, sometimes leaving vehicles stranded mid-operation. Zeldin said the new guidance will extend that timeline significantly.
‘Massive Deregulation’
Loeffler said the new policy will save America’s 1.8 million family farms an estimated $727 million annually.
“This is massive deregulation,” she said. “It’s solving a huge, long-standing issue that has gone on for 15 years.”
Rollins called the announcement “a big deal” for producers already struggling with higher costs and frequent downtime.
“We’re doing God’s work,” she said. “This is how we return power to the people and get the strangulation of overregulation out of everyday mom-and-pop small business owners’ lives, especially our farmers.”
While much of the call centered on agriculture and freight, Zeldin emphasized the rule’s importance for the passenger transportation industry.
“This was one of the concerns we heard from bus operators,” Zeldin told Bus & Motorcoach News. “It’s a safety concern when a bus is forced to park unexpectedly on the side of the road for an extended period of time. That’s all a product of poor government policy that didn’t think through the consequences.”
Phil Streif, of Vandalia Bus Lines in Caseyville, Illinois, told Bus & Motorcoach News in a separate interview that the change is the result of years of advocacy to bring operators’ perspectives to federal regulators. Streif began contacting the EPA five years ago, warning that the four-hour repair window was “just not realistic” for the motorcoach industry.
“After countless meetings with EPA and CARB, we finally got relief,” Streif said, “but the question remained about existing fleets.”
That question led to additional negotiations — and resistance from some engine manufacturers — before regulators agreed to modify the rules for vehicles already in service.
Uncertainty over future federal regulations already has disrupted one engine maker’s plans. Cummins Inc., a manufacturer of diesel engines, announced this month the postponement of the launch of its new X15 diesel engine for heavy-duty trucks to late 2026.
Initially unveiled in February with features meeting 2027 EPA and CARB standards, the engine was set for pre-orders in mid-2025 and deliveries in 2026. A statement from Cummins touted the technology used in the X15.
“Selective Catalytic Reduction (SCR) is a widely accepted, proven technology utilized in many applications, and we are committed to working closely with the EPA and the select customers affected by SCR inducements. Together, we aim to provide regulatory certainty, greater flexibility, and the dependable solutions that contribute to the American economy.”
Ending a Safety Risk
Streif said two moments proved decisive in resolving the derating issue: meeting EPA’s Amy Kopin, “who strongly advocated for us,” and the change in agency leadership when Zeldin took over. “They came out early, promising a goal to reduce regulation and the red tape that makes our businesses more challenging to operate. After many exchanges, we made great progress, and now we’re finally at the finish line.”
The new rules give bus operators 40 hours before even a minor torque reduction — something Streif calls “a game changer.”
“There are so many things that run through your head when you see an inducement code and know you have four hours before the bus is essentially inoperable,” he said. “We’re moving the most precious cargo there is — people — and derating created a profound safety risk for our drivers and passengers.”
Streif recounted an incident just two weeks ago in which a bus in New Orleans began showing a DEF-related fault code. Mechanics attempted repairs, but the problem reappeared within hours, forcing the company to dispatch a replacement bus from Alabama to ensure passengers could return home on time.
“Something that could have waited until we got the bus back created an obstacle for us that we had limited options for,” he said.
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The industry’s challenge was compounded by the scarcity of repair shops for motorcoaches, especially in remote areas or during off-hours. “There were no signs that could predict when a sensor would go bad, so it was like rolling the dice every time a bus went out,” Streif said.
Streif credited the American Bus Association, United Motorcoach Association, and International Motorcoach Group with helping build the case for reform.
“With their help and many members’ feedback, we were able to collect hard data and surveys that provided factual statistics on the impact derates have,” he said. “Honestly, without the strength of these great organizations, we probably wouldn’t have the results we were able to achieve.”
Putting Focus on Bus Industry
The advocacy also exposed a gap in federal oversight. “When I initially reached out to the EPA, their response was, ‘Oh, we didn’t even consider buses,’” Streif said. “It’s been stated before that our industry has been left out in the past, but I think that’s going to change going forward.”
He said the industry will need to maintain its presence in regulatory discussions. “Although our industry is small, we all work together in a way that other industries don’t see. That’s what will make us successful as long as we continue to support one another.”
Ernst praised the EPA’s move, calling the previous guidelines “arbitrary” and harmful to productivity. She also tied the changes to broader Republican efforts to roll back regulations enacted during the Biden administration.
Zeldin said the change reflects a broader philosophy of governance.
“Today’s guidance bridges the gap between now and 2027, ensuring existing vehicles on the road and in the field are just as dependable,” he said. “We’re both protecting human health and the environment and the people who depend on diesel engines to do their job.”
The EPA said no additional agency approval will be required for manufacturers to implement the new software changes.
For Streif, the new timeline — 40 hours before a small torque derate, then 200 hours before a 50 mph limit — is one the industry can live with. “On flat stretches we won’t see any impact,” he said. “I think we can all live with that.”
This article is reprinted with the permission of Bus and Motorcoach News. Read the original post here.
