Paccar will update engine software on MX-11 and MX-13 powertrains across Peterbilt and Kenworth trucks, following revised US Environmental Protection Agency (EPA) guidance on diesel exhaust fluid (DEF) inducements. The changes raise the final inducement speed limit from 5 mph to 25 mph and extend the component fault window from four to 160 hours.

DEF inducements are speed and power restrictions that activate when a vehicle’s emissions system detects a fault, including low DEF levels or degraded selective catalytic reduction system performance. The mechanism is designed to prompt drivers to address the issue rather than continue operating with inadequate emissions control.

Trucks built after 20 July 2026 will receive the updated software at the factory; those built after 2018 can obtain it at Peterbilt and Kenworth dealerships. Vehicles with faulty emissions components remain required to undergo service to maintain EPA compliance regardless of the revised thresholds.

The update reflects revised EPA guidance rather than a change to emissions standards, and the requirement to address system faults remains unchanged. Extending the window from four to 160 hours provides fleets with greater flexibility to manage servicing without the operational impact of a severely speed-restricted vehicle.

Source: Paccar