PACCAR and Cummins roll out DEF derate software updates following EPA guidance changes

PACCAR and Cummins have initiated software updates for diesel engines to align with revised Environmental Protection Agency (EPA) guidance issued in August 2025, which increases the minimum speed threshold for diesel exhaust fluid (DEF) inducement from 5 mph to 25 mph. The changes aim to provide carriers and farmers with greater operational flexibility and uptime by extending the timeframe for addressing emissions system issues before power derates occur. Selective catalytic reduction (SCR) systems, which rely on DEF to convert nitrogen oxides into nitrogen and water, remain critical for meeting EPA emissions standards. Inducements are designed to ensure emissions compliance by reducing vehicle speed and power when faults are detected. PACCAR will deploy updated software for MX-11 and MX-13 engines, with factory installations beginning July 20 for new trucks and dealership updates available for vehicles built after 2018. Cummins is rolling out updates for over 1.5 million engines across multiple model years, including certain 2017 models, with production updates starting in mid-August for on-highway engines and planned for 2027 for off-highway applications. The updates cover all EPA-certified on-highway engines using SCR technology and extend to EPA/EU-certified off-highway engines as well. PACCAR and Cummins join Daimler Truck North America, which began rolling out similar updates in February for approximately 330,000 in-service vehicles with DD15 and DD13 engines (model years 2021–2025). The EPA’s revised guidance also permits the replacement of urea-quality sensors with nitrogen oxide sensors, further supporting compliance and operational efficiency.