DEF Act

The Diesel Engine Flexibility Act establishes a ten-year regulatory stability period for diesel engines used in on-road vehicles, non-road equipment, and heavy-duty trucks. During this time, the Environmental Protection Agency is prohibited from issuing new or stricter emission standards beyond the 2007 and 2010 rules for on-road vehicles, or the Tier 4 rules for non-road engines, unless specific exceptions for repairs or fraud enforcement apply. After the decade concludes, any new regulations must include a five-year delay before taking effect and must consider the financial and operational impacts on vehicle owners and manufacturers. The bill also provides legal protection for manufacturers using specific guidance documents to manage engine performance and monitor fluid quality without facing penalties.