To passively regenerate a catalyzed DPF, which strategy is most likely?

• A. Driving at speeds above 45 mph (72 km/h) for at least 20 minutes
• B. Idle at low speed for 60 minutes
• C. Stop-and-go cycles
• D. Parked engine cranking only

Answer: (A)

Passive regeneration happens when the exhaust temperatures stay high enough long enough for the soot in the filter to burn off automatically, helped by the catalyst in a catalyzed DPF. The way to reliably achieve this is to keep the vehicle at higher highway speeds so the exhaust heat rises and is sustained, allowing the soot to oxidize without needing special interventions. Driving at speeds above 45 mph for about 20 minutes provides the steady, elevated exhaust temperature and adequate flow that promote this automatic clean-out.

Idle at low speed for an hour doesn’t heat the exhaust enough, so regeneration won’t occur. Stop-and-go cycles can cause temp fluctuations and may trigger active regeneration, but they’re not as reliable for passive regeneration, and the temps may not stay high enough. Parked engine cranking only doesn’t move exhaust, so temperatures stay too low for regeneration to happen.