The U.S. Environmental Protection Agency (EPA) recently announced a proposed rule to address Diesel Exhaust Fluid (DEF)-related engine deratements that can suddenly limit vehicle speed or shut down diesel-powered vehicles and equipment. Under the proposal, EPA would eliminate deratements and vehicle speed restrictions for newly manufactured highway engines and vehicles, replacing them with visible and/or audible alerts that would allow operators to continue operating until they can safely address the underlying problem.
The proposal is not yet final. The EPA will hold a 45-day public comment period and a public hearing, and is also seeking comment on whether it should develop guidance allowing manufacturers to make similar changes for vehicles and equipment already in service. ABA will review the proposal and evaluate opportunities to engage in the rulemaking process on behalf of the motorcoach industry.
“ABA welcomes EPA’s announcement proposing further action to address DEF-related deratements that can create serious safety, reliability, and operational challenges for motorcoach operators,” says Fred Ferguson, ABA’s President & CEO. “ABA has consistently supported reforms that reduce unnecessary and sensor-related derates, improve equipment reliability, and allow operators to address emissions-system issues safely without stranding passengers or creating roadside hazards.”
In August 2025, EPA issued new, clear guidance calling on engine and equipment manufacturers to revise DEF system software in existing vehicles and equipment to massively reverse deratements that were harming farmers and truckers.