The three regen types
Passive regeneration happens at highway speeds when exhaust temperatures naturally climb above 550°C and soot burns off without intervention. Active regeneration is initiated by the ECM injecting extra fuel during the exhaust stroke to heat the DPF while the truck is driving. Forced regeneration is a technician-commanded event with the truck parked, used only when the soot load is too high for active regen to complete.
When forced regen is the wrong answer
If a truck needs forced regens repeatedly, something else is wrong: a failed EGR cooler, leaking injectors, a plugged DOC, or a soot sensor that is lying about load. Forced regens mask the underlying failure and eventually thermally damage the DPF substrate. Fix the cause, not the symptom.
Ash cleaning is not regeneration
Regen burns off soot (carbon), which becomes CO2 and leaves the tailpipe. Ash is the inorganic residue from engine oil additives and never burns off. Every DPF eventually needs professional ash cleaning around 200,000 to 400,000 miles depending on duty cycle. Explain this to customers before they think they were sold a bad part.