Cold Weather Diesel Reliability Act of 2025

This bill requires the Environmental Protection Agency (EPA) to allow manufacturers of certain diesel vehicles to temporarily disable engine power-reduction or shutdown features during extreme cold, and to grant year-round exemptions from diesel exhaust fluid system requirements for vehicles in very cold regions.

Sec. 3, Definitions: Defines key terms: "Administrator" means the EPA Administrator; "covered manufacturer" means the maker of a covered vehicle or its engine; "covered vehicle" means an on-highway diesel vehicle or nonroad diesel equipment.

Sec. 4, Diesel engine emissions relief in cold weather regions: (a) Within 180 days, the EPA must revise regulations to let covered manufacturers suspend engine derate or shutdown functions triggered by emissions faults when temperatures are at or below 0°C, provided the engine returns to normal operation above 0°C and maximum performance is needed to prevent danger, equipment failure, or loss of essential transport in remote areas. (b) Within 180 days, the EPA must grant a year-round exemption from diesel exhaust fluid system requirements for any covered vehicle primarily operated north of 59° north latitude, or that encounters prolonged freezing conditions making diesel exhaust fluid use impractical. The exemption covers any requirement for engine derate or shutdown due to diesel exhaust fluid system issues.

Sec. 5, Rule of construction: Nothing in this bill waives compliance with Clean Air Act emissions standards except for the temporary cold-weather mode under section 4(a) and the diesel exhaust fluid system exemption under section 4(b).