EPA Tells Truck Makers to Stop Forcing Limp Mode for Low DEF

The Drive

9 hours ago

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The United States Environmental Protection Agency is on a roll when it comes to undoing past regulations and directives. Now, EPA Administrator Lee Zeldin is urging truck and engine manufacturers to do away with forced speed and power losses due to low diesel exhaust fluid levels. In his announcement at the Iowa State Fair, a key event humming with agricultural workers who have long voiced their negative opinions of modern diesel emissions systems, Zeldin called the software-imposed restrictions 'unacceptable' and 'unnecessary.'
There certainly would have been a time when such a move was surprising for the EPA, but the Trump Administration is conducting an about-face from its predecessors on environmental matters. It was Zeldin who, less than two weeks ago, announced the agency's intentions to stop regulating greenhouse gas emissions. He claimed that as a victory for industry, while this latest decision aims to champion everyday drivers and equipment operators.
'We have heard loud and clear from small businesses across the United States that the current DEF system is unacceptable. It is unacceptable that farmers, truckers, construction workers, and many other small businesses continually experience failures of diesel-powered equipment when they need it most—costing millions of dollars in lost productivity,' Zeldin insisted. 'Today, we are responding to those concerns by calling on manufacturers to take action to update their software and eliminate the unnecessary sudden loss of power and frustrating shutdowns that too many Americans have experienced.'
To explain it quickly, in case you aren't familiar: Most modern diesel engines rely on DEF for a process called selective catalyst reduction (or SCR). This fluid, which is a solution made from urea and deionized water, is injected into the exhaust stream to reduce nitrogen oxide (NOx) emissions. It's used in everything from heavy-duty pickup trucks to semis, tractors, excavators, and so on. DEF is sold in stores as well as at the pump at some fuel stations. Blue DEF
While DEF serves the clear purpose of improving emissions, many people malign it and everything that comes with it. The federal government estimates that hundreds of thousands of drivers have removed their trucks' emissions equipment altogether to avoid using DEF, citing performance and reliability concerns. Such modifications have been the cause of major fines and penalties dished out to diesel aftermarket companies in recent years.
For their part, manufacturers have made DEF a non-negotiable part of engine operation to meet restrictions put in place by past versions of the EPA. Even though DEF-related 'limp mode' was never mandated by the federal government, companies use the method to prevent people from running their vehicles and equipment without the solution. The EPA says diesel pickups are typically capped at 45 miles per hour once they've reached critically low DEF levels.
New EPA requirements taking effect in model-year 2027 state that new diesel trucks for road use cannot be engineered to force sudden and severe power loss after running out of DEF. Additionally, the EPA says it's issuing new guidance that was 'developed in collaboration with manufacturers' to make the necessary software changes for vehicles already in use. It's a sweeping move, then, applying to both used and new trucks. Caleb Jacobs
What's arguably most relevant to this announcement is that nothing will stop drivers or operators from running without DEF altogether. If their vehicle or machine's performance isn't limited when levels run low, many are unlikely to refill it at all. Some will see that as a win, while others will view it as a major loss.
The Drive has reached out to Ford, General Motors, and Ram for comment. I'll update this story when or if they respond.
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