The invention relates to a method for controlling the temperature of an NOx controlling component in an exhaust after treatment system of an internal combustion engine. The NOx controlling component has inner surface portions defining an interior component space through which exhaust gases are arranged to flow in order to be NOx controlled, and has outer surface portions facing away from the interior component space. The method comprises the step of: controlling the temperature of at least a portion of the NOx controlling component by a heat transfer medium arranged outside of the outer surface portions. The invention also relates to an exhaust after treatment system and a vehicle with such a system.