EPA Proposed Amendments to MY 2027+ Heavy-Duty NOx Program

Source: EPA – https://www.epa.gov/regulations-emissions-vehicles-and-engines/proposed-rule-amendments-and-nonconformance-penalties

BACKGROUND

On July 8, 2026, EPA Administrator Zeldin signed a proposed rule, "Amendments and Nonconformance Penalties for Model Year 2027 and Later Heavy-Duty Highway Engines and Amendments to Inducement Provisions for SCR-Equipped Diesel Engines."

The proposal substantially revises several compliance provisions of the Biden-era "2023 Final Rule" while explicitly retaining the MY 2027 emission standards and test cycles.

OVERVIEW & TIMING OF PROPOSED AMENDMENTS

The proposed amendments apply to medium- and heavy-duty engines, with the DEF-related changes also applicable to non-road engines. These include:

 (1) Emission-Related Warranty: Full Rollback to MY 2026 Periods

(2) Regulatory Useful Life: Three-Year Delay to MY 2030

(3) New Nonconformance Penalties (NCPs) for Medium and Heavy HDE Diesel

(4) SCR Inducements: Derates Replaced by Visible/Audible Notifications (we have covered that topic previously – https://mobilitynotes.com/epa-demands-manufacturer-data-as-it-expands-action-on-def-system-failures/)

WHAT'S NOT CHANGING

(1) Emission Limits

(2) Implementation date (except for useful life)

(3) Test Cycles (FTP, Low load cycle) and 2-Bin Off-Cycle In-use testing

(4) Averaging, banking and trading (ABT) architecture

MAIN PROPOSED AMENDMENTS OF THE HD LOW NOX RULE

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WHAT NEXT?

EPA has requested comments through over 50 questions. These were due by August 29, 2026. Virtual public hearings were scheduled for July 29–30, 2026.

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