EPA moves to stop Alaska's cold from shutting down diesel engines

The fluid that scrubs diesel exhaust can freeze — and when it does, an engine may throw false faults or cut its own power, sometimes stranding the vehicle. Where help can be hundreds of miles off, that becomes a safety problem. On Tuesday, the EPA proposed writing a fix into federal emissions policy.

Alaska operators told the agency that extreme cold can freeze diesel exhaust fluid, or leave it partly thawed, then force engines into power-limiting "derates." The EPA now proposes requiring manufacturers to build DEF freeze protection into new heavy-duty diesel engines, and to replace some emissions-related power cuts with visible or audible warnings instead.

The agency is seeking comment on Alaska-specific tweaks: whether warnings should switch off below 12 degrees, whether to allow exemptions by region or equipment type, and whether to let manufacturers modify engines already in use.

The proposal grows partly out of Sen. Dan Sullivan's Cold Weather Diesel Reliability Act, which would direct the EPA to account for cold-weather operation and prevent automatic shutdowns caused by emissions faults in freezing conditions. Alaska's Department of Transportation and Public Facilities has said the problem hits plows, graders, rural airport equipment and freight routes — machinery whose reliability, it argues, is a matter of life safety.

The rule is still a proposal. The EPA is taking comments through Aug. 29 and will hold virtual public hearings July 29 and 30.