Which regeneration approach is passive?

• A. Perform an active regen
• B. Do nothing
• C. Allow passive regen
• D. Replace the DPF

Answer: (C)

Regeneration of a diesel particulate filter occurs to burn off accumulated soot. The approach that is passive happens automatically during normal operation when exhaust temperatures are high enough to oxidize the soot, so no extra action is taken by the driver or ECU. This is why allowing passive regeneration is the best answer: it relies on the car’s usual operation and the physics of exhaust heat to clean the filter without an active intervention.

In contrast, an active regeneration is when the engine control system forcefully raises the exhaust temperature (for example, by altering fuel delivery or timing) to burn off soot, which is an active, deliberate intervention. Do nothing would mean no regeneration occurs at all, which isn’t a regeneration approach. Replacing the DPF is a maintenance action, not a regeneration method.