Paccar, Cummins roll out DEF derate software updates

A Paccar MX-13 engine. The parent of Kenworth and Peterbilt will offer updated software for vehicles equipped with MX-11 and MX-13 engines. (Paccar Inc.)

Paccar and Cummins have begun rolling out software updates that incorporate revised diesel exhaust fluid inducement parameters, lifting the minimum speed for trucks before DEF tanks must be refilled or sensors repaired.

The updates follow revised guidance from the Environmental Protection Agency in August 2025. EPA issued the guidance to offer carriers and farmers greater flexibility and uptime.

Selective catalytic reduction technology uses DEF to convert nitrogen oxides into nitrogen and water, supporting compliance with EPA emissions standards.

Inducements are the built-in safeguards on trucks and tractors that ensure emissions systems function appropriately by cutting vehicle speed and power should issues be detected.

From 5 mph to 25 mph

Under the revised guidance, the speed limit in final inducement will be increased to 25 mph from 5 mph, and the time to reach final inducement 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 trucks dating to model year 2017, the company said July 6.

Columbus, Ind.-based Cummins has begun offering the updates on some model-year 2026 production engines, with implementation timing varying by engine platform and model year. Additional model-year 2026 on-highway engines are expected to incorporate the calibration changes in 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 engines and newer, she added.

The updates are available for all EPA-certified on-highway engines that utilize SCR technology, while for off-highway applications, the changes apply to EPA-certified engines as well as EPA/EU engines that utilize SCR technology, the spokeswoman said.

“We appreciate EPA’s engagement with industry stakeholders and view the revised guidance as an important step toward addressing customer concerns in a practical, compliance-focused way,” Brett Merritt, engine business president, said in a statement. “Cummins has acted to support reliable implementation of these updates, help 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 equipped 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 obtain the updates at Peterbilt and Kenworth dealerships.

Paccar and Cummins followed Daimler Truck North America in rolling out the software update.

DTNA said June 22 it began rolling out the update in February for about 330,000 in-service vehicles with DD15 engines (model years 2021-2025) and DD13 engines (model years 2022-2025).

Updates for Freightliner and Western Star trucks are set to continue throughout 2026.

Freightliner and Western Star vehicles equipped 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 2010 model-year EPA mandates. DEF is a nontoxic, colorless and odorless solution comprising 32.5% urea and 67.5% deionized water.

Industrial urea manufacturing involves the chemical reaction of ammonia and carbon dioxide, most cost-efficiently using natural gas as the feedstock for the former.

Engines will still require DEF. The slowdown “induces” the driver to correct the issue, typically by refilling the DEF tank, repairing a faulty sensor or component, or performing a regeneration cycle.

But in March, EPA approved a guidance update that allows truck manufacturers to replace urea-quality sensors with nitrogen oxide sensors