An aftertreatment system of an internal combustion engine is disclosed. The aftertreatment system includes in a sequence along the exhaust pipe, a lean NOx trap and a particulate filter. An air/fuel ratio sensor is located upstream of the lean NOx trap and downstream of the turbine outlet to determine the air/fuel ratio during a regeneration process (DeNOx) in the lean NOx trap. A NOx sensor is located downstream of the lean NOx trap or downstream of the particulate filter, to determine NOx in the exhaust pipe. A turbine temperature is determined in accordance with a first means, and a temperature during a desulphation process (DeSOx) in the lean NOx trap is determined in accordance with a second means. At least one of the first and second means for determining a temperature may be a temperature sensor.