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The United States Environmental Protection Agency has changed its tune on diesel trucks under the current administration. Whereas previous versions of the EPA pursued massive penalties and even criminal fines for those who violate the Clean Air Act, Administrator Lee Zeldin has instead made deregulation a major focus. He already ordered manufacturers to stop forcing immediate limp mode on vehicles when diesel exhaust fluid runs low, and now, the EPA could take it a step further by eliminating the power and speed restrictions completely.
The EPA announced this on Tuesday with a strongly worded press release. In it, the agency said it’s “demanding information” from the top 14 manufacturers of on-road and off-road vehicles that use DEF systems. Specifically, it’s seeking info regarding warranty claims, failure rates, and repairs on model years 2016, 2019, and 2023 to determine if emissions system-related issues are concentrated on one generation of equipment or spread out. Manufacturers could face additional inquiries or penalties if they don’t provide the requested data within 30 days.
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
The EPA’s previous edict about DEF-related power and speed restrictions was significant, but this would be much more so. Historically, truck and agricultural equipment manufacturers would derate engine performance immediately when running low on DEF. Zeldin ordered that these limitations be put off from the 2027 model-year onwards, allowing diesel pickups to run normally for 4,200 miles or 80 hours with low DEF levels before being governed to 45 mph. The biggest potential change this time around is best summed up by a line from the EPA’s press release, which states, “It is being thoroughly assessed whether derates may no longer be necessary for compliance.”
Should the EPA decide that new diesel pickups no longer need limp mode to force drivers to fill their DEF tank, it would be major news. As it stands, those derates are the reason why many users add DEF to their trucks; the environmental concerns aren’t strong enough to outweigh the complaints. Diesel truck drivers have long spoken out against DEF and related emissions control systems for tanking reliability, fuel economy, and performance, so if they aren’t forced to refill it to get the most performance out of their trucks, you can pretty much bet that they won’t.
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From running point on new car launch coverage to editing long-form features and reviews, Caleb does some of everything at The Drive. And he really, really loves trucks.
