Mack and Volvo Trucks North America outline DEF derate software update schedules

Volvo Trucks North America (VTNA) and Mack Trucks have announced staggered rollout plans for revised diesel exhaust fluid (DEF) inducement software updates, following updated guidance from the U.S. Environmental Protection Agency (EPA) issued in August 2025. The revisions aim to provide carriers and farmers with greater operational flexibility and uptime by easing restrictions tied to DEF-related engine derates.

Starting in May 2026, new trucks produced by both brands have shipped with the updated software already installed. VTNA incorporated the changes into its D13 VGT and D13 TC engines for the refreshed VNL and VNR models, which received major overhauls in January 2024 and March 2025, respectively. Similarly, Mack equipped its Pioneer and Anthem flagship on-highway tractors—launched in April 2025 and June 2025—with the MP13 engines running the revised software.

The updated inducement parameters increase the final speed limit during DEF-related derates from 5 mph to 25 mph and extend the time before full inducement is triggered for component-related issues. These changes apply to DEF system faults such as low DEF levels, faulty sensors, or failed regeneration cycles.

VTNA and Mack plan to expand the software updates to model-year 2024 and newer vehicles by the end of summer 2026. The rollout will then extend to all post-2014 model-year vehicles by the second quarter of 2027, with coverage for eligible post-2010 models completed by the end of 2027.

The EPA’s revised guidance follows a broader federal review of emissions regulations under the current administration, which has proposed eliminating DEF-related engine derates entirely. Instead, future compliance may rely on visual or audible notifications rather than performance penalties. This proposal was included in a notice of proposed rulemaking on NOx tailpipe emissions standards.

Other major OEMs have also begun deploying DEF derate software updates. Daimler Truck North America (DTNA) started rolling out updates in February 2026 for approximately 330,000 in-service vehicles equipped with Detroit DD15 and DD13 engines from model years 2021–2025. Updates for Freightliner and Western Star trucks are ongoing throughout 2026. Paccar and Cummins began distributing updates in July 2026, covering over 1.5 million engines in medium- and heavy-duty trucks, including certain model-year 2017 units. Paccar’s Kenworth and Peterbilt brands will offer updates for MX-11 and MX-13 engines, with factory installations for trucks built after July 20, 2026, and dealership updates available for post-2018 models.

Selective catalytic reduction (SCR) systems, which require DEF to reduce NOx emissions, were mandated for 2010 model-year trucks to meet EPA standards. DEF—a solution of 32.5% urea and 67.5% deionized water—remains a required fluid, though the inducement system’s stricter penalties are being relaxed to improve uptime.