A Paccar MX-13 engine. The parent company of Kenworth and Peterbilt will offer updated software for vehicles with MX-11 and MX-13 engines. (Paccar Inc.)
July 7, 2026, 5:50 p.m., EDT
Table of Contents
Key Takeaways:
- The EPA policy increases the final request speed from 5 mph to 25 mph and extends timelines for correcting emissions system problems.
- Cummins plans updates to more than 1.5 million engines across multiple model years, with rollout varying by platform and application.
- Paccar and Daimler Truck North America are implementing similar updates for new and in-service vehicles through 2026.
Paccar and Cummins have begun rolling out software updates that include revised diesel exhaust injection parameters and raise the minimum speed for trucks before DEF tanks need to be refilled or sensors repaired.
The updates follow revised guidance from the Environmental Protection Agency in August 2025. EPA issued the guidance to provide more flexibility and uptime for shippers and farmers.
Selective Catalytic Reduction (SCR) technology uses DEF to convert nitrogen oxides into nitrogen and water, helping to meet EPA emissions standards.
Incentives are built-in protection devices in trucks and tractors that keep emissions systems functioning properly by reducing vehicle speed and power if problems are detected.
From 5 mph to 25 mph
Under the revised guidance, the speed limit at final notice will be increased from 5 mph to 25 mph and the time to reach final notice for component-related issues will be extended.
Cummins is offering updates for more than 1.5 million engines in medium- and heavy-duty trucks, including certain 2017 model year trucks, the company said July 6.
Columbus, Indiana-based Cummins has begun offering the updates to some 2026 model year production engines, with implementation timing varying depending on engine platform and model year. Additional model year 2026 on-road engines are expected to incorporate the calibration changes into production beginning in mid-August, a spokeswoman told Transport Topics on July 7.
For off-highway applications, the updated calibrations are planned for model year 2027 and newer engines, she added.
The updates are available for all EPA-certified on-highway engines with SCR technology, while the changes for off-highway applications apply to both EPA-certified engines and EPA/EU engines with SCR technology, the spokeswoman said.
“We appreciate EPA’s commitment to industry stakeholders and view the revised guidance as an important step in addressing customer concerns in a practical and compliance-oriented manner,” Brett Merritt, president of the engine business, said in a statement. “Cummins has acted to support the reliable implementation of these updates, helping customers and operators reduce unnecessary downtime and continue to meet emissions requirements.”
MX-11, MX-13 engines
Kenworth and Peterbilt parent company Paccar will offer updated software for vehicles with MX-11 and MX-13 engines, the company said July 6.
Trucks manufactured after July 20 will have the software installed at the factory, the parent company said. Trucks built after 2018 can receive the updates at Peterbilt and Kenworth dealers.
Paccar and Cummins followed Daimler Truck North America in rolling out the software update.
DTNA said on June 22 that it began rolling out the update in February to approximately 330,000 in-service vehicles with DD15 engines (2021-2025 model years) and DD13 engines (2022-2025 model years).
Updates for Freightliner and Western Star trucks are scheduled to continue throughout 2026.
Freightliner and Western Star vehicles with Detroit engines are already shipping with the updated software.
What is DEF?
SCR technology, and therefore the need for DEF, was introduced to meet EPA regulations for the 2010 model year. DEF is a non-toxic, colorless and odorless solution consisting of 32.5% urea and 67.5% deionized water.
The industrial production of urea involves the chemical reaction of ammonia and carbon dioxide, with natural gas being the cheapest raw material for the former.
Engines still require DEF. The slowdown “causes” the driver to correct the problem, typically by refilling the DEF tank, repairing a faulty sensor or component, or performing a regeneration cycle.
But in March, the EPA approved a guidance update that allows truck manufacturers to replace urea-grade sensors with nitrogen oxide sensors
https://www.ttnews.com/articles/paccar-cummins-def-updates
