Cold Weather Diesel Reliability Act of 2025

Allows diesel vehicles and engines used in very cold regions to continue operating when cold-weather sensor faults would otherwise trigger engine derates or shutdowns and creates year-round exemptions from certain diesel exhaust fluid (DEF) system requirements for vehicles that operate in prolonged freezing conditions or primarily north of 59° N. The Environmental Protection Agency must change regulations within 180 days to permit these temporary operational modes and to set conditions for restoring normal emissions controls when temperatures rise, while preserving existing emissions standards except for the specified cold-weather exceptions.