PACCAR Releases MX-11 and MX-13 Engine Software Updates Following EPA Derate Change

PACCAR announced that Kenworth and Peterbilt will implement software updates for trucks equipped with MX-11 and MX-13 engines that reflect the EPA’s newly revised guidance on Diesel Exhaust Fluid (DEF) inducements. (Source)

These software updates are intended to reduce unnecessary downtime by increasing the final inducement speed limit from 5 MPH to 25 MPH and extending the time before a truck reaches the final inducement stage for component-related or DEF quality issues from 4 hours to 160 hours.

Trucks built after July 20, 2026 will have the software installed at the factory. Meanwhile, software updates are available for Kenworth and Peterbilt trucks built after 2018.

EPA DEF Derate & Inducement Guidance Changes

In August 2025, the EPA issued a proposal to engine and equipment manufacturers outlining a tiered strategy that gradually limits vehicle performance rather than rapidly reducing vehicle speed to 5 mph. The revised DEF inducement guidance is a protective measure that gradually reduces speed and power when the emissions system detects an issue.

When the Selective Catalytic Reduction (SCR) system detects a low DEF level or a DEF system fault, the truck’s engine control system triggers an inducement. In the past, this meant drivers only had 4 hours before their vehicle speed dropped to 5 MPH. Under the new EPA guidance, operators now have 160 hours to address emissions system component faults or DEF quality issues before the truck reaches the final inducement stage, and the final speed limit increases to 25 MPH. This gives drivers more time to safely reach a service location before the final speed restriction takes effect.

PACCAR MX-11 & MX-13 Engine Software Updates

These software updates do not eliminate the need for Diesel Exhaust Fluid. DEF still remains essential for proper emissions system operation and helps protect your vehicle’s critical components, including the DEF injector. While installing the software updates is optional, trucks that do not receive them will continue to operate under the previous DEF derate strategy and will not benefit from the additional time or higher speed limits.

All affected MX-powered trucks must continue to comply with applicable EPA emissions requirements. Fleets must address emissions component issues and complete necessary repairs to maintain compliance.