2009 Glaval Titan Engine problems

This is a glaval bus on a gmc chassis, with a diesel engine. We have problems with the engine goes into its regeneration cycle. This causes excessive smoke and fumes to enter the passenger compartment of the bus. It has been to joe ball gmc in pittsburgh for service including reprogramming of the computer and for replacement exhaust parts. When the regeneration I son the drivers and passengers complain of the smoke and fumes. I have also contacted the gm customer service center regarding this concern. *Tr