A method pertaining to an SCR system for cleaning of exhaust gases from an engine including a dosing unit (250) to supply a reducing agent to an exhaust duct (240): Determining (s340) whether there is an undesired temperature level of the dosing unit (250). If one is found, removing (s360) warmed reducing agent from the dosing unit (250) and supplying it to the exhaust duct (240). Calculating (s350) and removing an amount of reducing agent based on a prevailing temperature of the dosing unit (250), or removing warmed reducing agent. Also a computer programme product containing programme code (P) for a computer (200; 210) for implementing the method. Also a device of an SCR system and a motor vehicle (100) which is equipped with the device are disclosed.