Comments close on EPA’s DEF rule; which way will it go?
The people have spoken on DEF changes. Now it waits for the EPA decision. The post Comments close on EPA’s DEF rule; which way will it go? appeared first on FreightWaves .
The public comment period on the federal proposal known as the "DEF rule" has concluded after receiving nearly 200 submissions with varied opinions on potential modifications to the Environmental Protection Agency (EPA) regulation. Published in the Federal Register on July 14, the proposal had a brief 45-day comment window, which closed last week, although some comments continued to be posted through Tuesday.
The proposal, referred to as the DEF (Diesel Exhaust Fluid) rule, aims to eliminate or significantly alter the "deratement" of an engine, a feature facing criticism for slowing vehicles when sensors detect inadequate or poor-quality DEF supplies. Three EPA actions within a year have sought to address deratements and other DEF-related issues: August 2025 guidance, March 2026 guidance, and the Federal Register proposal.
The key proposal in the Federal Register seeks to replace deratements with "audible and visual signals," alerting users of DEF-mandated equipment of low DEF levels or empty tanks, as opposed to a gradual engine slowdown. The EPA has already softened earlier deratement requirements through guidance released to engine manufacturers in August 2025 and March 2026.
While these guidance documents opened the door to increased use of NOx sensors and shortened emission-related warranty periods, they still retained the use of deratements. Manufacturers argue that DEF is highly effective in reducing NOx emissions, contributing to engine performance and fuel efficiency. However, environmental groups criticize the proposal for weakening provisions related to useful life requirements, emissions warranties, SCR inducement systems, and nonconformance penalties, arguing that these changes undermine the EPA's responsibility to protect public health.
The Truck and Engine Manufacturers Association (EMA) supports the deratements modification, stating that the August 2025 guidance is sufficient, but expressing concern over the potential impacts on nonroad equipment manufacturers.
Written by urgent.news from FreightWaves's reporting — not their text. Machine-written — may contain errors; check the original before relying on it.
