Regeneration Process of the Diesel Particulate Filer (DPF)
There are two types of regeneration that can occur: passive and active. Passive regeneration happens naturally when the heat of the exhaust burns off the soot. Active regeneration becomes necessary when the temperature is too low to completely burn off the soot. It is initiated by injecting fuel into the exhaust automatically. No driver interaction is needed. If soot continues to accumulate in the filter however, a parked regeneration is required. The driver is alerted to this through the indicator lamps on the instrument panel.

HIGH IDLE REGENERATION PROCEDURE Heavy Duty Engines
DFP Lamp Function DPF Indicator Lamp (Diesel Particulate Filter) From time to time, the yellow DPF Regeneration Lamp (shown above) may come on indicating that the soot level is elevated. Driving on the highway or having the engine under load will allow the filter to self-clean. If the light starts to flash, the driver will need to pull the truck over and initiate a high idle regeneration, following the steps to the right. If a truck is received with the DPF light on, follow the steps to the right.	Start High Idle Regeneration Regeneration Switch The engine needs to be warm (approximately 180F).  It is best to do this immediately after stopping. (Other OEM engine powered units may not need to reach a threshold exhaust temperature before they can begin the regeneration process.) 1. With the truck running, set the park brake, put the transmission in neutral and depress and release the clutch pedal. 2. Verify no other codes in the system (i.e. no check engine light) 3. Depress the Regeneration switch (shown above) for approximately 4 seconds.  The rpm will increase to about 1600. 4. Engine will bring up the temperatures and will then initiate regenerating the filter.	Regeneration Continued Hot Exhaust Temperature Indicator 5. Approximately 20-40 minutes later the engine will complete the regeneration and the engine will return to Idle / 600 rpm. 6. The hot exhaust temperature indicator lamp (shown above) may remain on.  This is an information lamp.  No driver action is required and the truck may be driven, other then caution of were the truck is parked Parked Regeneration will stop if the key is turned to the off position, the truck is put into gear or the parking brake is released. Refer to the “Instrument & Controls Identification” & “Engine & Clutches” sections of the vehicle driver’s manual for further information.
(Source: Detroit Diesel)