Photo via FreightWaves
Heavy-duty truck manufacturer PACCAR announced updated software on July 6, 2026 that raises the limp-mode speed threshold for diesel exhaust fluid systems in its vehicles. The change increases the maximum operational speed during DEF system malfunctions from 5 miles per hour to 25 miles per hour, a significant adjustment that alleviates a long-standing frustration for owner-operators who have faced stranding on highways when sensor anomalies trigger reduced-power modes.
According to industry sources, the modification reflects part of a broader rollback in diesel emissions enforcement. The adjustment represents a notable shift in regulatory approach, allowing trucks greater operational capability when experiencing DEF system issues rather than forcing complete operational restrictions. This change reduces the economic impact on trucking operations while vehicles are in limp-mode conditions.
The policy shift comes amid evolving environmental regulations and ongoing industry discussions about balancing emissions compliance with practical operational constraints. PACCAR's decision signals industry movement toward more flexible enforcement standards, particularly as stakeholders continue to debate the costs and benefits of existing diesel emissions control mandates.
