DPF (Diesel Particulate Filter)

A Diesel Particulate Filter captures soot particles from the exhaust so they are not released. Because the filter fills over time, it must periodically raise its own temperature high enough to burn the accumulated soot to ash — a process called regeneration.

Passive regeneration happens naturally when exhaust temperatures are high enough, typically during sustained highway running. Active regeneration is triggered by the engine management system when soot load rises, and needs the vehicle to keep running under load for the cycle to complete.

This is why duty cycle determines DPF trouble. Vehicles doing short urban trips with frequent idling never get hot enough for passive regeneration and often have active cycles interrupted by shutdown, so soot accumulates until the filter blocks. Fleets seeing repeated DPF warnings usually have a routing problem rather than a component problem.