HJS's CB² (catalytic bypass burner) system comprises a DPF, a primary catalytic converter (DOC II) that basically generates the heat required to regenerate the filter, and a preheating unit. The function of the preheating unit is to bring the primary catalytic converter up to operating temperature. The preheating unit comprises a diesel oxidation catalyst (DOC I), an electric heating element, and an HC doser. The electric heating element brings DOC I up to operating temperature when the exhaust-gas temperatures are particularly low. The HC doser doses and injects diesel into the exhaust gases in a controlled manner to use the two DOCs as catalytic burners. The diesel fuel oxidizes in these catalysts and releases heat. The exhaust gases in the primary flow section and in the preheating unit are controlled and directed in line with the required operating conditions by means of an exhaust flap built into the primary flow section. The HJS Aftertreatment Control Unit (ACU) monitors the operating conditions and coordinates interaction between the system components.