Cold Weather Diesel Reliability Act of 2025

Summary

Allows the EPA to revise emissions rules so diesel manufacturers can temporarily suspend engine derates or shutdowns caused by emissions-control faults when ambient temperature is at or below 0°C, and creates year‑round exemptions from diesel exhaust fluid (DEF) system requirements for diesel vehicles that primarily operate north of 59°N or that face prolonged freezing or impractical DEF use. EPA must issue the regulatory changes within 180 days, and the bill clarifies that all other Clean Air Act emissions standards remain in force except for these narrow, specified carve-outs.

• EPA must revise rules within 180 days to allow limited suspension of emissions‑related engine derates/shutdowns at or below 0°C.
• Only covered manufacturers may authorize the temporary suspension of derates or shutdowns, and normal emissions controls must resume above 0°C.
• EPA must create year‑round exemptions from DEF requirements for vehicles primarily operated north of 59°N or in prolonged freezing conditions.
• Vehicles granted DEF exemptions are protected from derate/shutdown triggers tied to DEF system faults or absence.
• The Act does not broadly change Clean Air Act emissions standards; it creates two narrow carve‑outs for cold weather and DEF impracticality.
• Covered vehicles include on‑highway diesel vehicles and nonroad diesel equipment; 'manufacturer' uses the Clean Air Act definition.
• No new funding or tax changes are included; implementation occurs through EPA rulemaking.
• Intended benefit is safer, more reliable diesel operation in extreme cold and remote areas, but may increase short‑term emissions under the allowed exemptions.