EPA Proposes to Eliminate DEF Deratements

EPA Proposes to Eliminate DEF Deratements

Recently, the Environmental Protection Agency (EPA)published the full text of a proposed rule that would eliminate diesel exhaust fluid (DEF) deratements — the forced speed and power reductions that trucks and other diesel equipment impose when an SCR system detects a fault. In place of a hard deratement, EPA's proposal would require audible and visible alerts,letting operators keep working until they can safely address the problem. EPA estimates the change could save the trucking industry $12 billion, or up to$6,000 per new truck purchased. The proposal also scales back the emissions-warranty requirement finalized under the Biden administration,holding coverage on the heaviest engines closer to current levels — 100,000miles or five years — rather than the 450,000 miles or 10 years set to take effect with model year 2027. A third piece adds non conformance penalties,roughly $1,000 to $7,000 per engine, which would let manufacturers sell 2027engines that temporarily fall short of the new NO x standards while working through technical delays. The underlying 2027 NO x standards themselves are not being rolled back; EPA says the proposal preserves roughly 90% of the associated emissions reductions.

Taken together, the three pieces mark a broader retooling of the 2023 heavy-duty NOx rule rather than a narrow fix. EPA is framing deratement relief as the headline consumer-facing win, but the warranty scale-back and non conformance-penalty mechanism are new compliance flexibilities for manufacturers that weren't part of earlier deratement-focused proposals, and they change the cost and risk picture on the manufacturer side of the transition.

For Nebraska agriculture, deratements and SCR reliability have been a recurring frustration for members running diesel-powered equipment,and Nebraska Farm Bureau has been building a response to EPA that addresses both deratement relief and the broader question of whether DEF/SCR systems are well suited to agricultural equipment at all. The warranty and non conformance-penalty provisions raise a related issue worth watching as manufacturers gain relief on warranty exposure and a compliance buffer during the transition, equipment owners will want clarity on what that means for coverage on equipment already in the field. Comments on the proposal are due by August 29, 2026, and EPA has scheduled virtual public hearings on July 29 and30. Nebraska Farm Bureau's team is reviewing the rule and will continue updating members.

‍