House bill would shield EPA DEF guidance for 10 years

Truck drivers have seen a string of EPA moves on diesel exhaust fluid systems over the past year, and Congress is now trying to keep those changes from flipping back.

A new House bill, HR9618, the Diesel Engine Flexibility (DEF) Act, would create a “statutory safe harbor” for EPA diesel emission guidance issued in 2025 and 2026 for 10 years. The bill would also bar the EPA from setting emission standards stricter than the existing 2007 and 2010 diesel emission standards during that period.

The proposal would cover guidance tied to DEF inducements and sensors. It would also require the EPA, after the 10-year freeze, to give at least five years’ lead time before any stricter emission standards take effect, and those standards would have to remain in place for at least three model years before any further tightening.

The bill says the EPA would have to consider downtime, derates and shutdowns, durability, repair and replacement costs, resale values, financing and dealer inventories, nationwide consistency, and harmonization across engine families and vehicle categories.

The DEF Act says it does not allow permanent disabling of emission control systems and does not exempt vehicles or equipment from existing emission standards.

Reps. Michelle Fischbach, R-Minn.; Julie Fedorchak, R-N.D.; Don Davis, D-N.C.; Jack Bergman, R-Mich.; and Brad Finstad, R-Minn., introduced the bill. Fischbach said in a statement that the DEF Act provides a “vital, 10-year legal shield” for agricultural and trucking industries while keeping existing emissions standards in place.