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Key insights
- Cummins offers revised calibrations for more than 1.5 million engines in medium- and heavy-duty trucks.
- PACCAR updates MX-11 and MX-13 engine software for eligible Peterbilt and Kenworth trucks.
- Both updates increase the final speed limit from 5 mph to 25 mph for covered heavy-duty truck applications.
- The updates provide greater operational flexibility, but emissions compliance and repair requirements remain.
Cummins and PACCAR are updating diesel engine software to give truck operators more time to correct certain diesel exhaust fluid system problems before vehicles reach the most restrictive operating limits.
The updates follow the U.S. Environmental Protection Agency’s revised guidance on DEF incentives, which are protective measures that reduce vehicle speed and performance when problems with the emissions system are detected. The changes do not remove emissions regulations and vehicles with issues with emissions components will still require repairs.
Cummins is updating certain engine calibrations to give operators more time to make necessary repairs and reduce unnecessary downtime associated with DEF incentives. The revised calibrations extend the time before certain DEF-related incentives occur and increase final incentive speeds under certain circumstances. The updates extend the time to initial and subsequent downgrade events under certain manipulation and DEF quality conditions, while increasing the final downgrade speed from 5 mph to 25 mph.
Cummins says the updates are intended to provide additional operational flexibility while meeting emissions system requirements.
Cummins has begun offering revised calibrations for more than 1.5 million engines in medium-duty and heavy-duty trucks, including certain truck applications beginning with model year 2017 and certain motorcoach applications beginning with model year 2018. Timing varies by engine platform and model year. Customers may contact a local Cummins distributor or dealer to schedule available updates.
PACCAR also announced updated software for vehicles equipped with PACCAR MX-11 and MX-13 engines. Trucks manufactured after July 20, 2026 will have the software installed at the factory, and trucks built after 2018 will be eligible for the updates at Peterbilt and Kenworth dealers.
These changes increase the final demand speed limit from 5 miles per hour to 25 miles per hour and extend the time period for component or fluid quality problems from four hours to 160 hours before the final demand speed limit is reached.
The announcements from Cummins and PACCAR follow a June 18 announcement from Daimler Truck North America detailing how the OEM is equipping Freightliner and Western Star vehicles with Detroit engines with updated DEF incentive software aligned with EPA guidelines. DTNA said its newest Detroit-powered Freightliner and Western Star vehicles are already shipping with the updated software, and the company began rolling out the same software in February 2026 to approximately 330,000 in-service vehicles with DD15 engines from the 2021 to 2025 model years and DD13 engines from the 2022 to 2025 model years.
https://www.act-news.com/news/engine-makers-update-def-software-to-reduce-truck-downtime/
