Comments close on EPA’s DEF rule; which way will it go?

The public comment period on the federal proposal that has come to be seen as the “DEF rule” has come to a close, with almost 200 submissions spanning the gamut of opinions on possible changes in the Environmental Protection Agency (EPA) regulation. The proposal, published in the Federal Register by EPA July 14 after earlier signaling of its intentions, had a relatively short window for comment, just 45 days. That ended last week though some comments continued to be posted on the comment’s website through Tuesday. It’s come to be known as the DEF (Diesel Exhaust Fluid) rule because among other goals, the EPA proposal would seek to eliminate or significantly change one aspect of the use of DEF that has come in for criticism: the “deratement” of an engine, where it slows the vehicle if sensors pick up that DEF supplies are inadequate or are of poor quality. There have been three EPA actions in a little more than a year that are attempt to tackle the issue of deratements and other issues that users of DEF have criticized: the August 2025 guidance , the March 2026 guidance and the more formal proposal in the Federal Register that was the basis for th