S3135-119

What This Bill Does

This bill, the Cold Weather Diesel Reliability Act of 2025, requires the EPA to revise Clean Air Act regulations within 180 days to address two cold-weather problems for diesel vehicles and equipment. First, it authorizes manufacturers to suspend engine derate or shutdown functions that are triggered by emissions control system faults when temperatures are at or below freezing (0 degrees Celsius), provided normal emissions controls resume above that temperature. Second, it grants year-round exemptions from diesel exhaust fluid (DEF) system requirements for vehicles operating primarily north of 59 degrees north latitude or in conditions where DEF systems are impractical due to prolonged freezing. The bill preserves all underlying emissions standards outside of these specific exemptions.

Who Benefits and How

Diesel vehicle and equipment operators in cold regions (Alaska, northern U.S.) benefit by avoiding dangerous engine shutdowns and power reductions in extreme cold. Trucking and transportation companies operating in cold climates benefit from uninterrupted vehicle operation. Diesel engine and vehicle manufacturers gain the legal authority to program cold-weather overrides into their engines. Rural communities and emergency services benefit from reliable diesel transportation in cold weather. The oil and gas, mining, and logging industries that rely on diesel equipment in remote cold environments benefit from equipment reliability.

Who Bears the Burden and How

The EPA bears the regulatory burden of revising its Clean Air Act regulations within 180 days. Environmental interests bear the cost of reduced emissions control enforcement during cold weather periods and year-round exemptions in extreme cold regions. DEF manufacturers and suppliers may see reduced demand in exempt regions. The general public in cold regions bears a potential air quality impact from suspended emissions controls, though the bill preserves underlying emissions standards.

Key Provisions

• EPA must revise regulations within 180 days to authorize manufacturers to suspend engine derate/shutdown functions at or below 0 degrees Celsius (Section 4a)
• Only covered manufacturers may suspend derate/shutdown functions (Section 4a)
• Year-round DEF system exemption for vehicles operating north of 59 degrees N latitude (Section 4b)
• Year-round DEF system exemption for vehicles in prolonged freezing conditions making DEF impractical (Section 4b)
• All underlying emissions standards remain in effect outside these specific exemptions (Section 5)
• Engine must return to normal emissions control operation above 0 degrees Celsius (Section 4a)