DEF Act: New Legislation Proposes 10-Year Repair Protection

DEF Act Advances With 10-Year Protection for Truck Repairs

A House subcommittee has advanced a bill that could change how diesel exhaust fluid problems are handled across the trucking industry. The Diesel Engine Flexibility Act, also called the DEF Act, would protect certain EPA-approved software updates, sensor changes, and repair methods for 10 years.

Supporters say the bill could reduce harsh engine derates and shutdowns caused by faulty DEF sensors. These problems can leave trucks stuck on the road or unable to finish a load.

However, the DEF Act would not fix existing trucks on its own. It would not end all DEF rules or remove every engine derate. The bill would also place wider limits on future diesel emissions rules.

DEF Sensor Failures Can Create High Costs

DEF system problems can create major costs for truck drivers and carriers.

A bad sensor can trigger warning lights, reduce engine power, or limit truck speed. In some cases, the engine may still be able to run. Even so, the emissions system may force the truck into a severe derate.

That can lead to missed delivery times, towing bills, repair costs, and lost miles.

Owner-operators may face the greatest risk. One disabled truck can stop their entire business.

A truck in the shop is not earning money. The owner may still have to pay for insurance, truck payments, permits, and other fixed costs.

A breakdown can also lead to hotel bills, missed loads, storage fees, and late delivery claims.

Large fleets may be able to move freight to another truck. Still, they can face road service costs, late freight, extra labor, and fewer trucks ready for work.

What the DEF Act Would Do

The DEF Act would create a 10-year legal safe harbor.

That protection would apply to companies and repair providers that follow EPA diesel emissions guidance issued in 2025 and 2026.

The safe harbor could cover approved software updates, sensor changes, repair methods, recalls, and better diagnostic tools.

The goal is to give companies more legal certainty.

Manufacturers may be more willing to issue updates if they know an approved change will not later be treated as illegal emissions tampering.

Repair shops may also gain clearer rules when they work on DEF systems.

The DEF Act would allow EPA to keep approving software fixes, recalls, and diagnostic changes that match the guidance.

Supporters say the law is needed because future EPA leaders could change or remove the guidance. Putting the policy into law would make it harder to reverse.

DEF Act Would Not Change Trucks Right Away

The DEF Act would not make an instant change to trucks already on the road.

Manufacturers would still need to design and approve software updates. They would also need to decide which engines and truck models could receive them.

Some trucks may qualify. Others may not.

The result could depend on the truck’s age, engine type, emissions hardware, and past repairs.

The bill would not force manufacturers to provide free repairs. It would not require every truck to receive a new sensor or software update.

It would also not repay drivers or carriers for money already lost because of DEF system failures.

Truck owners would still need to ask the engine maker, dealer, or repair shop whether an approved update is available.

This is an important limit in the DEF Act. The measure would protect legal fixes, but it would not require every company to offer one.

Drivers Could Have More Time Before a Derate

EPA guidance issued in 2025 gave engine makers more options for handling DEF-related faults.

Under one approved path, the first torque cut would not begin until 650 miles or 10 hours after the fault.

A final 25-mph speed limit would not begin until 8,400 miles or 160 hours.

Those limits would not apply to every truck by default.

A manufacturer would need to use the approved plan and make the update available for a certain truck or engine.

Still, a longer warning period could help truck drivers.

A driver may have more time to reach a truck stop, terminal, dealer, or repair shop before the truck loses major power.

That could reduce the risk of being stuck on the shoulder or losing speed in heavy traffic.

For owner-operators, even a few extra hours could lower towing costs and reduce lost income.

DEF Act Could Give Repair Shops More Clarity

The DEF Act could also help independent repair shops.

Emissions repairs can carry legal risk. Shops must be careful when changing software, sensors, or engine controls.

The bill would offer more protection when a shop follows an approved EPA method.

That may make it easier for some truck owners to get work done outside a dealer network.

However, the bill would not make illegal repairs legal.

DEF deletes would still be banned.

Defeat devices, illegal tuning, and other changes that turn off emissions controls would also remain illegal.

A legal software update is not the same as a DEF delete.

That difference would remain important for drivers, fleets, repair shops, and compliance staff.

Safety Departments May See Benefits

A severe engine derate can create a safety problem.

A truck that loses power at highway speed may have trouble keeping up with traffic. The risk can be higher on hills, curves, narrow roads, or routes with little shoulder space.

Longer warning times could give a driver more control over where the truck is taken for service.

That may reduce roadside stops and emergency tows.

Fleet safety teams may also have more time to plan repairs before a truck becomes hard to move.

Still, the DEF Act would not set a new safety rule. Its effect would depend on what updates manufacturers release and how those updates work in real trucks.

DEF Act Includes Broader Emissions Limits

The DEF Act includes rules that go beyond sensor problems.

The bill would limit EPA from placing some stricter motor vehicle emissions rules into effect for 10 years.

The language covers heavy-duty engines, trucks, and other vehicles.

This part of the bill could have a much wider effect on trucking.

It may shape future engine design. It could also affect truck prices, repair needs, and the types of engines sold in the United States.

The bill may also affect state emissions plans.

California and other states have tried to use rules that are stricter than federal standards. The DEF Act could create legal questions about how those programs are approved or enforced.

For trucking companies, the broader limits may affect long-term buying plans, used truck prices, dealer stock, loans, and resale values.

Future Rules Would Need More Lead Time

The DEF Act would require more lead time for future emissions rules.

New standards would need at least three model years of use. They would also need five years before taking effect.

Supporters say this would give engine makers and truck builders more time to prepare.

It could also help fleets, dealers, and repair shops plan for new rules.

Small carriers may gain the most from longer lead times. Many owner-operators and small fleets cannot replace trucks as quickly as large carriers.

The bill would also direct EPA to consider costs such as downtime, repair bills, truck replacement, loans, resale values, dealer stock, and vehicle supply.

DEF Act Has Not Become Law

The DEF Act was introduced by a bipartisan group of House lawmakers.

The group includes Representatives Michelle Fischbach, Julie Fedorchak, Don Davis, Jack Bergman, and Brad Finstad.

A House Energy and Commerce subcommittee advanced an amended version by voice vote on July 14, 2026.

That vote moved the bill forward, but it did not make it law.

The measure must still pass the full committee, the House, and the Senate. It would then need the president’s signature.

Until those steps are complete, the bill will not create new legal rights or change current truck repair rules.

What the DEF Act Could Mean for Truck Drivers

The main possible benefit of the DEF Act is more time before a truck enters a severe derate.

That could help drivers reach a safe location or repair shop.

It may also reduce roadside breakdowns, towing bills, missed loads, and lost pay.

Owner-operators could gain more control over where and when repairs are made. Fleets may see fewer emergency road calls and less unplanned downtime.

However, the DEF Act would not guarantee that every truck gets an update.

It would not remove DEF systems, end all derates, or make illegal emissions changes legal.

The bill remains a proposal. Its final effect would depend on the language that becomes law and whether engine makers offer approved fixes for trucks already in service.