The Environmental Protection Agency on Wednesday proposed eliminating DEF-related engine deratements for new highway and nonroad engines and replacing forced speed restrictions with staged warning alerts, the agency says. The proposal would remove automatic “limp mode” power reductions tied to diesel exhaust fluid system faults and rely on alerts so operators can continue work until safe repairs are possible. FEATURED IMAGE ALT: DEF-related engine deratements — Trucks and freight moving on a U.S. highway
What the EPA proposed
Under the draft rule, EPA would remove automatic DEF-related engine deratements and attendant speed limits for new highway engines and new nonroad equipment, including farm machinery. Instead of forcing engines into a severe power-limited mode when certain DEF fault codes appear, manufacturers would provide alerting systems that notify operators and allow continued operation until a safe repair window is available, the agency said.
The agency also proposes modifying certain emissions warranty and compliance timelines set in a 2023 rule, offering manufacturers additional flexibility and time to meet updated standards while keeping required pollution controls in place, according to EPA statements. EPA officials describe the changes as intended to reduce operational disruptions without eliminating emissions protections.
DEF-related engine deratements and the new alert approach
EPA air chief Aaron Szabo said the patchwork of DEF fault codes can trigger deratements that leave vehicles immobile or crawling. Szabo told reporters the agency found more than 200 potential fault codes tied to DEF systems that, under current rules, can cause severe power reduction. “We’re both making the products more reliable and decreasing the impact from DEF,” Szabo said. “And we’re also bringing down the price of the whole supply chain by reducing the cost of these new trucks,” he added, per EPA remarks.
The staged-alert model would notify drivers and equipment operators at multiple thresholds so they can plan repairs without immediately losing full mobility. EPA says the approach aims to balance continuity of operations with ongoing emissions monitoring and enforcement tools.
Impact on truckers, farmers and supply chains
EPA projects the rule would produce roughly $12 billion in industrywide savings and estimates savings of up to about $6,000 per new truck; the agency describes those numbers as modeling-based projections. These figures are agency forecasts based on specific modeling assumptions and will be scrutinized through the formal rulemaking record and public comments.
Supporters including some trucking and farm groups argue automatic deratements can be disruptive during harvests or time-sensitive freight moves. Secretary of Agriculture Brooke Rollins said the proposal “has shown the true cost of government overreach” and argued the changes would help rural operators who “feed, fuel, and clothe the nation.” Opponents warn reduced automatic protections could raise on-road emissions risks if alerting systems are ignored or poorly implemented.
Industry advocates say shorter downtime and fewer limp-mode incidents could lower logistics costs and reduce delayed deliveries that ripple through supply chains. Independent analysts say the size of those benefits depends on real-world repair behavior, enforcement, and whether manufacturers and fleets adopt reliable alerting and verification practices.
BODY IMAGE ALT: DEF-related engine deratements — Equipment and highway incident image for context
Emissions tradeoffs and NOx impact
EPA says the proposal would relax some warranty requirements from the 2023 rule but preserve nearly 90% of the planned NOx emissions reductions from that earlier regulation. The agency framed this as maintaining most environmental benefits while easing operational constraints for operators and manufacturers.
Experts caution that the reported $12 billion savings and the “nearly 90%” retention of planned NOx reductions are agency projections that depend on modeling choices, assumptions about repair and maintenance behavior, and compliance. These estimates will be evaluated through the public-comment record and any supporting technical submissions; they are not independent verifications.
Reactions and political framing
EPA officials highlighted reliability and cost. Aaron Szabo said the proposal targets unnecessary outages and cost drivers while keeping emissions controls in place. Secretary Brooke Rollins and other allied officials framed the measure as a rollback of burdensome mandates, arguing it reduces costs for farmers and truckers.
Critics say the tradeoff could weaken near-term emissions enforcement. Some legal and policy analysts warned that alerts depend on timely action by fleets and regulators. The debate has political overtones: allied officials have linked the proposal to broader efforts to ease certain Biden-administration environmental rules, while opponents emphasize environmental safeguards.
Media reporting on the proposal noted outreach to the White House Office of Joe Biden for comment; Fox News Digital reported contacting that office as part of its coverage. Policymakers on both sides are expected to press for more data in the comment period.
Next steps and what to watch
The proposed change now enters standard rulemaking, including a public comment period and review of technical and economic evidence. Stakeholders can submit data and analysis challenging the EPA’s modeling or offering alternative assumptions; EPA will consider comments and may revise the proposal before any final rule.
Observers should watch for independent analyses that verify (or contest) the agency’s $12 billion savings estimate and the projected NOx outcomes, as well as any state or industry proposals that seek stricter verification, remote monitoring or backstop enforcement measures to ensure emissions goals are met.
Background
Diesel exhaust fluid (DEF) is used to reduce nitrogen-oxide emissions in modern diesel engines. When DEF systems register faults, existing rules in some cases require engines to reduce power or enter “limp mode” as a way to limit emissions while awaiting repair. The new EPA proposal would shift from automatic power limits to alert-driven responses for new engines and equipment, altering how compliance and operational continuity are balanced.
Frequently asked questions
What are DEF-related engine deratements?
DEF-related engine deratements are automatic power-reduction responses triggered when an engine’s diesel exhaust fluid system reports certain faults. Those deratements can force vehicles into a low-speed “limp mode” until repairs are made under current rules.
How much would the industry save under the EPA estimate?
EPA projects about $12 billion in industrywide savings and up to roughly $6,000 per new truck; these are agency projections based on modeling and assumptions that will be reviewed during the rulemaking comment period.
Will this change reduce planned NOx emissions cuts?
EPA says the update would preserve nearly 90% of the planned NOx reductions from the 2023 rule while changing some warranty and compliance timelines. Independent outcomes depend on manufacturer compliance, monitoring, and how alert systems are implemented.
Sources: Reporting and sourcing include Environmental Protection Agency statements and materials; Fox News Digital coverage. For primary agency materials, see the Environmental Protection Agency: epa.gov. For the media report cited in this story, see Fox News Digital: foxnews.com. Attribution: EPA projections and quoted remarks are from EPA officials; reporting on outreach to the White House Office of Joe Biden was reported by Fox News Digital.
