Originally Posted by TWP723
ReGen happens when the truck idles for periods of time or driven short periods. The system needs to regenerate itself due to lack of distance, so to speak, driving.
Regen occurs when the particulate filter reaches its designated soot mass (in grams) to initiate the process.
This is a constant process MEANING the particulate filter is always gaining soot mass while driving HOWEVER REGENERATION is not constant.
It also can be forced into regeneration by means of the dealer
When idling for long periods or doing stop and go and not getting up to speed for a period of time the truck in most cases will notify you to continue driving.
Limp mode is an entirely different animal. This can happen for 2 main reasons; 1) the truck is out of DEF fluid and is limiting its speed due to being out of compliance with emissions and 2) something is seriously wrong with the truck and to reduce damage the truck will limit its power levels and performance to keep it safe.