EPA Proposes End to DEF Derates, Receives Mixed Reception

The Environmental Protection Agency has proposed eliminating diesel exhaust fluid-related engine derates, replacing them with visual or audible notifications. This move is part of the Trump administration’s broader effort to revise Biden-era NOx regulations, aiming to reduce downtime and keep trucks operating. The proposal has received a mixed response, with carriers and the American Trucking Associations welcoming the change, while fuel marketers and truck-stop groups have expressed concerns that it could undermine the success of DEF technology in reducing emissions. The EPA’s intention is to offer carriers and farmers greater flexibility and uptime, following revised guidance on DEF inducement parameters announced in August 2025. The proposal builds on July 1 guidance from the EPA, instructing truck and engine manufacturers to offer customers the opportunity to repair DEF and other on-highway vehicle environmental control systems. The trucking industry has responded with a mix of support and criticism, with some advocating for a balanced approach that preserves environmental progress while improving equipment reliability. Selective catalytic reduction technology, which uses DEF to convert nitrogen oxides into nitrogen and water, has played a significant role in reducing emissions from modern diesel engines. However, engine derates triggered by emissions system issues can leave trucks stranded, highlighting the need for a solution that balances environmental concerns with operational efficiency. The proposal is part of the Trump administration’s ongoing rollback of Biden-era emissions regulations, with the EPA seeking to ease costs and reliability concerns for fleets and manufacturers. As the proposal moves forward, the trucking industry will be closely watching the developments, with some manufacturers already rolling out software updates to incorporate the revised DEF inducement parameters.