H.R. 6250 — Cold Weather Diesel Reliability Act of 2025

This section states congressional findings that (1) diesel vehicles are vital for critical transportation and emergency services in cold weather regions; (2) in rural regions with prolonged freezing conditions, diesel exhaust fluid storage, supply, and system functionality are frequently unreliable and logistically impractical year-round; (3) automatic engine shutdowns and power reductions due to emissions control malfunctions in extreme cold pose serious, life-threatening risks; and (4) emissions safeguards under the Clean Air Act were never intended to jeopardize human safety or impede critical mobility.

This section establishes definitions for terms used in the Act, including (1) Administrator, meaning the Administrator of the Environmental Protection Agency; (2) covered manufacturer, meaning the manufacturer (as defined in section 216 of the Clean Air Act, 42 U.S.C. 7550) of a covered vehicle or an engine of a covered vehicle; and (3) covered vehicle, meaning an on-highway diesel vehicle or nonroad diesel equipment.

This section directs the EPA Administrator, not later than 180 days after enactment, to revise Clean Air Act regulations applicable to covered vehicles and engines to (1) authorize covered manufacturers to suspend inducement-related engine derate or shutdown functions triggered by emissions control system faults when ambient temperatures are at or below 0 degrees Centigrade (0°C)—with the engine required to return to normal operation above 0°C and the suspension necessary to prevent occupational danger, equipment failure, or loss of essential transportation in remote areas—and prohibit any other party from suspending those functions; and (2) grant year-round exemptions from diesel exhaust fluid (DEF) system requirements, including associated derate or shutdown functions triggered by DEF system faults, for covered vehicles primarily operated north of 59 degrees north latitude or encountering prolonged freezing conditions that make DEF use impractical. (Thus, the changes provide operational relief for heavy-duty diesel engines in extreme cold, where emissions aftertreatment systems such as DEF-based selective catalytic reduction can freeze or fault, potentially stranding vehicles without roadside support.)

This section clarifies that nothing in this Act waives compliance with any emissions standard under the Clean Air Act except for (1) the temporary cold-weather operational mode authorized under section 4(a) and (2) the exemption from diesel exhaust fluid system requirements under section 4(b).