Mack Trucks and Volvo Trucks are rolling out updated diesel exhaust fluid (DEF) inducement software across their North American lineups, becoming the latest manufacturers to give fleets more breathing room before an emissions fault forces a truck to slow to a crawl. According to Truck News, the updates reflect revised EPA guidance that raises the final inducement speed from 5 mph to 25 mph and extends the repair window from four hours to as much as 160 hours.
For drivers, that difference is significant. A DEF inducement, commonly called a derate, kicks in when the emissions system detects a fault such as low DEF or a problem with the selective catalytic reduction (SCR) system, which uses DEF to cut nitrogen oxide (NOx) emissions. Under the old rules, a fault could drop a truck to 5 mph within hours, a sudden loss of power that carriers long argued was both costly and, on a rural interstate or a steep grade, potentially unsafe. The revised schedule gives operators far more time and speed to reach a service location.
An industry-wide shift, not a single-brand move
Mack and Volvo are joining a rollout that now spans nearly every major engine maker. Cummins and Paccar, the parent of Kenworth and Peterbilt, adjusted their software in early July, with Heavy Duty Trucking reporting the same 5-to-25 mph and 4-to-160-hour changes. Per Transport Topics, Cummins is offering updates for more than 1.5 million engines dating back to model year 2017, while Daimler Truck North America began its own rollout earlier in the year across roughly 330,000 in-service vehicles.
The common thread is EPA policy. The agency issued voluntary guidance allowing manufacturers to revise DEF inducement strategies, and in July 2026 proposed going further by eliminating mandatory DEF derates for new heavy-duty vehicles while keeping current NOx standards in place, as reported by Transport Topics. The EPA has estimated the broader proposal could save operators thousands of dollars per vehicle.
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