The U.S. Environmental Protection Agency (EPA) has proposed targeted changes to its model year 2027 heavy-duty engine rules that could reduce costs and give manufacturers more time to meet longer-term emissions requirements.

The proposal would retain current emissions-warranty periods for 2027 and later engines, delay longer regulatory useful-life requirements until model year 2030 and allow some manufacturers to pay nonconformance penalties while completing development of compliant engines. EPA also proposes replacing certain diesel exhaust fluid-related engine derates with visible or audible warnings.

EPA estimates the changes could save purchasers as much as $37 billion in warranty costs, including up to $6,000 per diesel vehicle, while preserving nearly 90% of the nitrogen oxide reductions projected under the original rule. The proposal could affect truck, engine, automotive-parts, farm-equipment and construction-equipment manufacturers.

“EPA’s proposal recognizes that environmental rules have to work in the real world,” said James Lee, managing director of public policy services for the Ohio Manufacturers’ Association. “More compliance flexibility can preserve emissions progress while reducing unnecessary warranty costs, production disruptions and equipment-price increases.”

Comments are due Aug. 29. 7/15/2026