Cold Weather Diesel Reliability Act of 2025

Cold-weather diesel relief for operators

If enacted, the EPA would have 180 days to change rules so diesel manufacturers can pause emissions-related engine derates or shutdowns when ambient temperatures are at or below 0°C. Only a covered manufacturer could suspend those functions, and engines would return to normal operation once temperatures rise above 0°C. The EPA would also have 180 days to allow a year-round exemption from diesel exhaust fluid (DEF) system requirements for vehicles mainly operated north of 59° north (shown by operation, domicile, or maintenance/dispatch records) or for vehicles that face prolonged DEF freezing or make DEF use impractical. That DEF exemption would also bar requirements to include engine derates or shutdowns tied to DEF absence, degradation, malfunction, or related sensors and control modules. The bill would define key terms (Administrator, covered manufacturer, covered vehicle) and say emissions standards still apply outside the cold-weather mode and DEF exemptions.