Regen is short for Regeneration and it is the process of cleaning the DPF of it’s particulate matter, or soot. The DPF has two sensors, one in from and one behind the DPF. As the DPF becomes clogged with soot and difference of pressure is sensed called the differential pressure. These sensors send the information to the engine ECM which decides if it is a good time to regenerate. The regeneration can take an average of 40 minutes to complete and must be done when the engine is at approximately 1200 rpm.
This regeneration can take place as you are driving down the highway. If for some reason the Regen is stop, either by depressing the clutch, brake or activating the engine brake, the ECM will try again when engine speeds exceed 1200 rpm. Problems arise when the Regen can not be completed, and the soot level reaches extreme measures, or clogs off more the 75% of the DPF. This is when the light on the dash comes on. If it is caught early enough, the technician can put the system into a manual Regen by means of a PC and allowing the Regen to complete it’s cycle, the driver can be back on the road within an hour or so. There are situations when a Regen can not be completed, but I will further describe them in a separate section.