DEF Act
- Sponsor
- Rep. Fedorchak, Julie [R-ND-At Large]
- Committees
- Energy and Commerce Committee (primary)
- Last action
- Jul 14, 2026
Bottom line
The bill aims to provide a decade of regulatory certainty for diesel engine manufacturers and operators by freezing current emissions standards and codifying specific EPA guidance related to emissions control systems.
What it actually does
This bill amends the Clean Air Act to establish a 10-year period of regulatory stability for on-road and nonroad diesel engines. It prohibits the Environmental Protection Agency (EPA) from promulgating more stringent emissions standards than those in effect as of January 1, 2025, for these categories. Additionally, it creates a safe harbor for certain emissions control practices (inducement strategies and diesel exhaust fluid quality monitoring) if they are consistent with specific EPA guidance documents issued in 2025 and 2026.
Proponents argue
Supporters argue this legislation provides crucial regulatory stability, reducing operational disruptions and compliance costs for businesses in the transportation, agriculture, and construction sectors. They contend it protects equipment durability, ensures national consistency for motor vehicle and engine requirements, and fosters economic predictability, allowing for long-term planning and investment.
Opponents contend
Opponents would contend that this bill halts progress on air quality improvements, potentially locking in older, less stringent emissions standards for a decade. They argue this could exacerbate pollution and public health issues, undermine the EPA's authority to update standards based on new science or technology, and slow the adoption of cleaner engine technologies.
The bill is relatively short and its core provisions are clearly stated, allowing an informed reader to grasp its implications within a reasonable timeframe.
Section 2, amending Clean Air Act Section 202(n)(1)
Guidance-Based Safe Harbor for On-Road Vehicles and Engines
This provision establishes a 10-year period, starting from the bill's enactment, during which certain practices related to inducement strategies and diesel exhaust fluid (DEF) quality monitoring will not be considered prohibited acts under the Clean Air Act. This applies to new and in-use motor vehicles and engines (including heavy-duty and light-duty) that comply with 2007 or 2010 emissions standards, provided these practices are consistent with specific EPA guidance documents (IACD-2025-10 and IACD-2026-05).
Supporters argue
Supporters argue this provision provides crucial certainty for manufacturers and operators, preventing costly retrofits or operational changes based on evolving interpretations of emissions rules and ensuring that current, widely adopted practices are protected.
Critics contend
Critics may argue that codifying specific guidance could inadvertently allow practices that, while technically compliant, lead to higher real-world emissions, or that it preempts the EPA's ability to adapt to new information or improve emissions control strategies.
Tradeoffs
This provision balances the industry's need for regulatory certainty and stability with the potential for slower adoption of more stringent emissions controls or the risk of locking in practices that may not be optimal for environmental protection.
Section 2, amending Clean Air Act Section 202(n)(2)(A)
10-Year Freeze on More Stringent On-Road Emissions Standards
For a period of 10 years, the EPA Administrator is prohibited from creating, revising, or implementing any regulation for new or in-use motor vehicles or engines that is more stringent than the 2007 and 2010 emissions standards. Exceptions are made for approving software updates, enforcing against defeat devices, implementing administrative requirements, and approving voluntary manufacturer actions that maintain compliance with existing standards.
Section 2, amending Clean Air Act Section 202(n)(2)(B) and (C)
Future Standard Lead Time and Required Considerations for On-Road Engines
After the 10-year regulatory freeze expires, any new or revised emissions standards for on-road vehicles and engines must meet specific criteria: they must apply for a minimum of 3 model years and take effect no earlier than 5 years after their promulgation. Furthermore, the EPA Administrator is required to consider several factors during rulemaking, including operational disruption, durability, resale value, costs to owners, the need for national consistency, and harmonization across various vehicle and engine categories.
Section 3, amending Clean Air Act Section 213(e)(1)
Guidance-Based Safe Harbor for Nonroad Vehicles and Engines
Similar to the on-road provision, this section establishes a 10-year safe harbor for specific practices related to inducement strategies, repair-related overrides, and diesel exhaust fluid (DEF) quality monitoring for nonroad vehicles and engines. These practices will not be considered prohibited acts under the Clean Air Act if they are consistent with specified EPA guidance documents (IACD-2025-10, IACD-2026-01, and IACD-2026-05) and apply to nonroad vehicles or engines complying with Tier 4 standards.
Section 3, amending Clean Air Act Section 213(e)(2)(A)
10-Year Freeze on More Stringent Nonroad Emissions Standards
For a period of 10 years, the EPA Administrator is prohibited from creating, revising, or implementing any regulation for new or in-use nonroad vehicles or engines that is more stringent than the Tier 4 standards. Similar to the on-road provision, exceptions are made for approving software updates, enforcing against defeat devices, implementing administrative requirements, and approving voluntary manufacturer actions that maintain compliance with existing standards.
Section 3, amending Clean Air Act Section 213(e)(2)(B) and (C)
Future Standard Lead Time and Required Considerations for Nonroad Engines
After the 10-year regulatory freeze expires, any new or revised emissions standards for nonroad vehicles and engines must meet specific criteria: they must apply for a minimum of 3 model years and take effect no earlier than 5 years after their promulgation. Furthermore, the EPA Administrator is required to consider several factors during rulemaking, including operational disruption, durability, resale value, costs to owners, the need for national consistency, and harmonization across various nonroad categories and engine families.
The bill defines the specific emissions standards (2007, 2010, and Tier 4) that serve as the baseline for the 10-year regulatory freeze by referencing particular sections of the Code of Federal Regulations (40 CFR 86.007-11, 86.010-18, 1039, and 1068) as they were in effect on January 1, 2025.
Section 2(n)(4)(A)-(B) and Section 3(e)(4)(B)
Why it matters:While it is standard legislative practice to define terms, the specific date reference (January 1, 2025) is a crucial detail that locks in the exact regulatory text, making it less flexible to minor administrative updates without triggering the bill's restrictions.
Case for: Supporters would argue this provides absolute clarity and precision regarding the baseline standards, preventing any ambiguity or shifting interpretations about which regulations are subject to the freeze.
Case against: Critics might contend that locking in a specific date prevents the EPA from making minor, non-substantive updates or clarifications to these baseline regulations, potentially creating unforeseen regulatory inflexibility.
Estimated impact: This provision establishes the precise regulatory floor for a decade, impacting all affected on-road and nonroad vehicles and engines by preventing any more stringent standards from being applied.
The bill defines "covered guidance documents" by referencing specific EPA internal designations and issue dates: IACD-2025-10 (August 11, 2025), IACD-2026-05 (March 26, 2026), and for nonroad engines, IACD-2026-01 (January 30, 2026). These documents outline the specific inducement strategies, repair-related overrides, and DEF quality monitoring practices that are granted a safe harbor.
Section 2(n)(4)(C) and Section 3(e)(4)(A)
Why it matters:It is standard legislative practice to reference external guidance or regulations. However, relying solely on internal agency designations without providing a summary or public link makes the bill's full operational effect less immediately transparent to a casual reader.
Case for: Supporters would argue that referencing these specific guidance documents ensures the safe harbor is precisely aligned with existing EPA interpretations and industry practices, providing targeted and clear relief.
Case against: Critics might argue that relying on external, potentially less accessible documents makes the bill's scope opaque to the general public and could make it harder to scrutinize the specific practices being protected.
Estimated impact: This provision precisely defines the operational practices related to emissions control systems that are protected from enforcement for a decade, directly impacting compliance strategies for manufacturers and operators.