EMA
The EPA has issued new guidance, eliminating the Diesel Exhaust Fluid (DEF) Urea Quality Sensor requirement for all diesel vehicles and nonroad equipment. According to the agency, its action will deliver $13.8 billion in total annual savings to American operators through reduced repair costs and restored productivity.
DEF systems have been required on nearly all on-road diesel trucks and much nonroad equipment since 2010 as part of selective catalytic reduction (SCR) technology used to reduce nitrogen oxide (NOx) emissions. However, faulty DEF sensors have triggered erroneous fault signals that force vehicles into speed deratements — in some cases slowing trucks to as little as five miles per hour — causing significant operational disruptions and economic hardship for truckers, farmers, bus operators, and others who depend on diesel-powered equipment.
EPA’s new guidance authorizes manufacturers to replace traditional Urea Quality Sensors with NOx sensors, which preliminary warranty data suggests are far less prone to generating the inaccurate fault readings responsible for most DEF-related deratements. EPA also said that installing approved NOx sensor-based software updates on existing diesel engines does not constitute illegal tampering under the Clean Air Act, consistent with the agency’s February 2026 Right-to-Repair guidance.
EPA’s action follows its August 2025 guidance, which significantly extended derate warning windows — giving heavy-duty truck operators up to 650 miles or 10 hours before any deratement begins, and allowing normal operation for up to 4,200 miles thereafter. EPA has also indicated it intends to issue a deregulatory proposal to eliminate all DEF deratements for new vehicles and engines.
