DEF Act: 10 Years of Legal Protection for EPA Diesel Emissions Guidance

On July 14, Representatives Michelle Fischbach, Julie Fedorchak, Don Davis, Jack Bergman, and Brad Finstad introduced the Diesel Engine Flexibility (DEF) Act, legislation that would protect agricultural and transportation businesses by building on the diesel emissions guidance recently issued by the U.S. Environmental Protection Agency (EPA).

The lawmakers said the EPA’s stringent engine shutdown requirements are costing farmers, truck drivers, and equipment operators both time and money. The DEF Act aims to strengthen monitoring capabilities by limiting unnecessary engine shutdowns and power derates while providing independent technicians with legal clarity to service their customers’ equipment.

By strengthening and codifying the EPA’s recent actions, the proposal seeks to reduce measures that could negatively affect the productivity of truck drivers and farmers. “Without congressional action, these improvements remain subject to future administrative changes,” the five lawmakers said.

DEF Act: 10-Year Legal Protection for EPA Guidance

Under the proposal, the DEF Act would provide a 10-year period of legal protection for the EPA’s diesel emissions guidance issued in 2025 and 2026. It would also allow the EPA to continue approving software updates, diagnostic system improvements, recalls, and other administrative actions that are consistent with that guidance.

In addition, the legislation would require future emissions regulations to include reasonable implementation timelines, including at least three model years of applicability and a minimum of five years before new standards take effect.

The bill also directs the EPA, when developing future emissions regulations, to consider measures aimed at reducing unnecessary engine shutdowns, power derates, and operational disruptions.

“The DEF Act provides a critical 10-year legal shield that protects our agriculture and trucking industries from unnecessary shutdowns, allowing supply chains to keep moving while maintaining current emissions standards,” Representative Fischbach said.

Representative Fedorchak added that farmers, truck drivers, and equipment operators should not be affected by unnecessary shutdowns that “have nothing to do with actual emissions.” She said the DEF Act is intended to create a stable regulatory framework for the next decade, providing manufacturers, operators, and independent technicians with the certainty they need to invest, innovate, and keep equipment operating without compromising emissions performance.

Without congressional action, these improvements remain vulnerable to future administrative changes. The Diesel Engine Flexibility Act would provide long-term regulatory certainty by reducing unnecessary downtime caused by faulty emissions sensors while preserving all existing emissions standards.