Paccar is updating the software on its MX-11 and MX-13 engines to align with revised EPA guidance intended to reduce unnecessary downtime caused by diesel exhaust fluid (DEF) inducements.
The updated calibration will be installed at the factory on new Kenworth and Peterbilt trucks built after July 20, 2026. The software will also be available through Kenworth and Peterbilt dealerships for trucks built after 2018 equipped with Paccar MX-11 or MX-13 engines.
The update follows the EPA guidance issued last summer, which requires "that all new diesel on-road trucks must be engineered to avoid sudden and severe power loss after running out of DEF." At the time, EPA had urged engine OEMs to update software to mitigate the issue for existing trucks and heavy equipment. Daimler Truck North America (DTNA) has done the same with its in-service DD13 and DD15 engines.
Under the new software, the final inducement speed limit increases from 5 mph to 25 mph. The update also extends the time before a vehicle reaches the final inducement stage for component-related or DEF fluid-quality issues, increasing the window from 4 hours to 160 hours.
The revised EPA guidance aims to reduce frustrating derates and disruptions while preserving compliance with federal emissions requirements. By allowing trucks to continue operating longer before reaching their final derate and increasing the minimum operating speed, the agency's recommendations aim to provide fleets additional time to schedule repairs without immediately sidelining vehicles.
Paccar said all MX-powered vehicles will continue to be subject to EPA emissions requirements, and trucks with malfunctioning emissions components must still be repaired to remain compliant.
