Senate Considers Cold Weather Diesel Reliability Act

The Senate Environment and Public Works (EPW) Committee held a hearing yesterday, September 16, to consider S. 3135, the Cold Weather Diesel Reliability Act of 2026. The legislation would authorize vehicle manufacturers to override the need for emissions-reducing Diesel Exhaust Fluid (DEF). DEF is used by selective catalytic reduction (“SCR”) systems installed in diesel vehicles and farm equipment to reduce nitrogen oxides (“NOx”) emissions. The legislation would effectively exempt vehicles operating in cold weather environments from DEF requirements.

SCR systems have helped to substantially reduce NOx emissions in the United States by 79% since 2010, according to the Transportation Energy Institute (TEI). Installation of these systems and use of DEF on nearly all heavy-duty vehicles and nonroad equipment has contributed to a 76% and 42% reduction in NOx emissions, respectively, accounting for 79% of total NOx reductions in the U.S. since 2010.

Recently, the U.S. Environmental Protection Agency (EPA) issued guidance to address operator concerns regarding engine “deratements” when DEF sensors detect a problem. EPA also proposed regulations to eliminate deratements altogether. However, SCR systems can experience significant and costly damage if operated without DEF, which deratements are intended to prevent.

NACS, along with NATSO and SIGMA, submitted comments to EPA regarding these issues, which have been shared with the Senate EPW committee along with the TEI report as context for yesterday’s hearing. The associations’ members are the primary retail and wholesale suppliers of DEF to the commercial trucking industry, the agricultural sector and the broader diesel equipment market, and make DEF available at more than 95% of the nation's truck stops. NACS appreciates that the Senate is considering this important issue.