The Cold Weather Diesel Reliability Act of 2026 directs the Environmental Protection Agency to change its rules so diesel vehicle and equipment manufacturers can temporarily disable automatic engine power-reduction or shutdown features that are triggered by emissions control problems when outdoor temperatures drop to 20 degrees Fahrenheit or below, with normal operation resuming once temperatures rise above that threshold. It also allows manufacturers to permanently suspend these emissions-related shutdown features for agricultural equipment, such as tractors and combines, and for on-highway or off-road diesel vehicles operated primarily north of 59 degrees north latitude, covering much of Alaska. The bill mainly benefits farmers and businesses in extreme cold-weather regions who rely on diesel engines for essential transportation, emergency response, and farm work, where such automatic shutdowns could create safety hazards or operational failures. The EPA must issue these regulatory changes within 180 days of the law's enactment. The bill specifies that it does not waive compliance with underlying Clean Air Act emissions standards, only the derate and shutdown mechanisms tied to certain sensor and system faults.