On August 12, 2025, the U.S. Environmental Protection Agency (EPA), under Administrator Lee Zeldin, announced new guidance aimed at addressing the widespread frustration with Diesel Exhaust Fluid (DEF) systems used in diesel-powered trucks and farm equipment. The updated rules, rolled out at the Iowa State Fair in Des Moines, are being celebrated by some in the agricultural and trucking industries as a relief from the sudden power losses and engine shutdowns caused by DEF system failures. However, for many farmers and truckers, the changes don’t go far enough, and the underlying issues with DEF systems, which are viewed as costly, cumbersome, and politically driven, remain unresolved.
A Welcome Change, but Only a Band-Aid
The EPA’s new guidance allows manufacturers to revise DEF system software to prevent the severe “derates” that can slow vehicles to a crawl (as low as 5 mph) when DEF runs out or sensors fail. For heavy-duty trucks, a fault now triggers a warning light with no performance impact for up to 650 miles or 10 hours, followed by a modest 15% engine power reduction for up to 4,200 miles. For non-road equipment like tractors, combines, and sprayers, there’s no power loss for 36 hours, followed by a 25% torque reduction for up to 100 hours, and a 50% reduction thereafter. Starting with model year 2027, all new diesel on-road trucks must incorporate these protections by design.
The trucking industry, represented by groups like the American Trucking Associations (ATA) and the Owner-Operator Independent Drivers Association (OOIDA), has praised the changes. ATA’s Patrick Kelly called the guidance a “common-sense solution” that avoids towing costs and downtime while preserving environmental benefits. OOIDA President Todd Spencer highlighted the flexibility, noting it helps truckers “finish their trips” and plan maintenance without being stranded by false sensor alerts. Similarly, the Small Business Administration (SBA) estimates the changes will save America’s 1.8 million family farms $727 million annually by reducing costly repairs and operational delays.
For farmers, the relief is tangible. “This announcement is a big deal, especially for our farmers and ranchers,” said USDA Secretary Brooke Rollins, pointing to the 30% rise in input costs and a $30 billion trade deficit as added pressures on the agricultural sector. Iowa Senator Joni Ernst echoed this sentiment, calling the guidance a “common-sense” fix that prevents tractors from halting in the middle of a field due to “Green New Deal-style regulations.”
The Deeper Frustration: DEF as a Symbol of Overreach
Despite the applause, many farmers and truckers argue the new guidelines are merely a patch on a fundamentally flawed system. DEF, introduced under the EPA’s Tier 4 emissions standards in 2004 and fully implemented by 2015, requires selective catalytic reduction (SCR) systems to reduce nitrogen oxide (NOx) emissions. While supporters claim DEF helps maintain air quality, operators see it as a costly burden that adds complexity, maintenance, and downtime to their already tight budgets.
Farmers, in particular, have long expressed their disdain for DEF. The fluid itself is an additional expense, often costing thousands of dollars annually for large operations. The SCR systems are prone to malfunctions, with repairs that can run into the thousands and leave equipment inoperable during critical planting or harvest seasons. Until the new guidelines are implemented, if a tractor runs out of DEF or a sensor fails, the machine can enter “limp mode,” severely reducing power and stranding operators in the field. Storage is another headache; DEF has a limited shelf life, freezes at 12°F, and degrades above 86°F, making it a logistical nightmare for rural operators. Contamination risks during refilling can further damage systems, leading to more downtime.
Truckers share similar grievances. The sudden power reductions caused by DEF faults can disrupt supply chains, delay deliveries, and rack up towing and repair costs. Many operators believe the systems reduce engine efficiency and fuel economy, further eating into their slim profit margins. DEF systems epitomize bureaucratic overreach, forcing farmers and truckers into costly, unreliable tech that cripples productivity.
A Political Scheme or Environmental Necessity?
The core of the opposition lies in the perception that DEF systems are less about real environmental protection and more about political agendas tied to climate change policies. Critics argue that the EPA’s mandates, rooted in the 2009 Endangerment Finding, prioritize “green dogma” over the practical realities of farming and trucking. Farmers, already operating at a loss in many cases, and truckers, working on razor-thin margins, resent bearing the financial burden of what they see as Washington’s hair-brained schemes.
The environmental benefits of DEF are also under scrutiny. While the EPA insists that SCR systems reduce NOx emissions, which is a contributor to air quality issues, many operators question whether the trade-off is worth it. The complexity and cost of DEF systems, they argue, outweigh the supposed environmental gains. Some even suspect the push for DEF is part of a broader political effort to phase out diesel entirely, pointing to the Biden administration’s 2024 electric truck mandates as evidence of an anti-diesel agenda.
The Real Solution: Scrap DEF Altogether
For many farmers and truckers, the EPA’s new guidance, while a step in the right direction, falls short of the ultimate goal: eliminating DEF systems entirely. “This is a welcome first step, but we’re hoping it signals a larger move toward getting rid of DEF,” is a sentiment we have seen across social media. The consensus among operators is that diesel machinery was more efficient, reliable, and affordable before DEF became mandatory. Removing the systems would cut maintenance costs, reduce downtime, and allow operators to focus on their work rather than managing a finicky emissions control system.
The EPA’s own statements acknowledge the “nearly universal” frustration with DEF, yet the agency stops short of dismantling the system, likely due to its commitment to emissions standards. The new guidance maintains that environmental benefits are preserved, but critics argue that a full repeal of DEF requirements would better balance economic and operational needs with air quality goals.
Looking Ahead: A Call for Common Sense
The EPA’s new DEF guidelines have sparked a mix of relief and skepticism. While the changes promise to ease the immediate pain of sudden shutdowns and save millions in costs, they don’t address the deeper issues of a system many see as flawed from the start. Farmers and truckers are calling for more than tweaks, as they want a return to machinery that prioritizes efficiency, affordability, and reliability over what they view as politically motivated regulations.
The new rules offer a temporary reprieve, but the fight is far from over. For now, operators are left hoping that the EPA’s willingness to listen signals a broader shift toward policies that support, rather than burden, the industries that keep America moving and fed. Until then, the call remains clear: if politicians want to push climate-driven mandates, they should foot the bill, or get out of the way.