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Friday, March 27, 2026
Today, EPA 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.
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