DPF regeneration modes explained

When it comes to diesel particulate filter (DPF) regeneration, there are three types: 

1. Passive -- This occurs when the load and speed of the engine produce temperatures greater than 350 degrees C, and it burns off the trapped soot as the vehicle operates. 
2. Active -- If the duty cycle does not produce high enough exhaust temperatures, the DPF becomes loaded with soot, which is indicated by its pressure sensors. Active regeneration is then required. During active regeneration, raw fuel is injected into the diesel oxidation catalyst (DOC) to achieve appropriate regeneration temperatures in the DPF. Neither active generation or passive regeneration require input from the vehicle operator, and no check engine light codes are shown the vehicle dashboards for either regeneration process.
3. Manual -- This type of regeneration occurs only when the vehicle is stationary, and it requires action on the part of the vehicle operator. The check engine light will illuminate on the vehicle dashboard, usually after an extended period of idling (when hydrocarbons build up and can cause overheating of the DPF).  The vehicle operator must set the park brake and enable the parked regeneration to begin. Engine rpm increases and raw fuel is injected into the exhaust gas at the exit of the engine to generate the appropriate regeneration temperatures. The stationary vehicle manual regeneration processes take about 30 minutes.

Information provided by Daimler Trucks North America