U.S. EPA Multi-Pollutant Emissions Standards for Model Year 2027 and Later Passenger Cars and Light Trucks

ENFORCEMENT TIMELINE

Phased application beginning with model year 2027 (production starting in late 2026)

Enforcement: Phased application beginning with model year 2027 (production starting in late 2026)

Overview

This federal emissions standard, finalized by the U.S. Environmental Protection Agency (EPA) in March 2024, covers passenger cars, light-duty trucks (SUVs, pickups, etc.), and medium-duty vehicles for model years 2027 through 2032. It originally required phased, substantial reductions in both greenhouse gas emissions (CO2, etc.) and criteria air pollutants (NMOG+NOx, PM, etc.). In February 2026, however, EPA under the Trump administration finalized a rule rescinding the 2009 Greenhouse Gas Endangerment Finding, which had served as the legal basis for the rule's GHG emissions standards—raising significant doubt as to the continued effect of the GHG provisions. Separately, on May 18, 2026, EPA published a proposed rule to delay the effective date of the Tier 4 criteria pollutant standards from model year 2027 to model year 2029.

Enforcement Timeline

March 2024: EPA publishes the final rule

February 2026: EPA finalizes a rule rescinding the 2009 Greenhouse Gas Endangerment Finding, raising significant doubt as to the legal basis for the GHG emissions standards

May 18, 2026: EPA publishes a proposed rule (Part 1) delaying the effective date of the Tier 4 criteria pollutant standards from model year 2027 to model year 2029

2026 (ongoing): EPA has also indicated it will separately reconsider the Tier 4 standards themselves (Part 2)

As of August 24, 2026: The status of both the GHG and criteria pollutant provisions remains uncertain, with litigation over the Endangerment Finding rescission ongoing

Related Regulations / Topics

U.S. EPA Greenhouse Gas Endangerment Finding Rescission Rule and the Tier 4 Emissions Standards Delay Proposal

In February 2026, EPA under the Trump administration finalized and published a final rule fully rescinding the 2009 "Greenhouse Gas (GHG) Endangerment Finding," issued under the Clean Air Act (CAA). Because the Endangerment Finding served as the legal foundation for all of EPA's authority to regulate GHG emissions from vehicles and factories (including the Clean Power Plan and vehicle GHG standards), this rescission has destabilized the legal basis for federal vehicle GHG regulation. In connection with this, on May 18, 2026, EPA published a proposed amendment rule (Part 1) to delay the effective date of the "Multi-Pollutant Emissions Standards" (Tier 4 criteria pollutant standards), which had applied to passenger cars and light trucks beginning with model year 2027, by two years to model year 2029.

Business Impact

Manufacturers exporting vehicles and components to, or producing locally for, the North American market are likely to face a significantly reduced sense of urgency around the previously anticipated shift toward electrification (EVs, PHEVs, HEVs). With the legal basis for the GHG emissions standards rescinded, the overall effectiveness of the rule may hinge on the outcome of litigation challenging the Endangerment Finding rescission. The proposed two-year delay to the criteria pollutant standards may also require companies to revisit their supply chain electrification and localization plans. Separately, companies should confirm the latest status of related programs, including IRA tax credit eligibility requirements.