Abstract: A method is disclosed for determining a current temperature of a heating element with a PTC thermistor property (PTC) with which a urea-water solution for cleaning the exhaust gas in an internal combustion engine of nitrogen oxides can be heated. According to the invention there is provision that a correction factor is formed from the quotient of a minimum resistance of the heating element and of a minimum resistance of a reference heating element, in that a resistance which is determined at a current temperature of the heating element is multiplied by the correction factor, and in that the current temperature of the heating element is determined from the corrected resistance value and a temperature dependence of the resistance of the reference heating element. The method according to the invention permits more precise determination and regulation of the temperature of the heating element.

Abstract: A method is disclosed for determining a current temperature of a heating element with a PTC thermistor property (PTC) with which a urea-water solution for cleaning the exhaust gas in an internal combustion engine of nitrogen oxides can be heated. According to the invention there is provision that a correction factor is formed from the quotient of a minimum resistance of the heating element and of a minimum resistance of a reference heating element, in that a resistance which is determined at a current temperature of the heating element is multiplied by the correction factor, and in that the current temperature of the heating element is determined from the corrected resistance value and a temperature dependence of the resistance of the reference heating element. The method according to the invention permits more precise determination and regulation of the temperature of the heating element.

Abstract: A method for operating a reagent dosing system (12), in which at least one dosing valve (14) doses a reagent upstream of at least one SCR catalytic converter (16) which is arranged in an exhaust-gas duct of an internal combustion engine (10), in which method the reagent, which is stored in a tank (28), is heated by means of a heater (30), and in which method a cavity (44) in the region of the heater (30) is detected on the basis of the evaluation of a characteristic variable of a measure of the heating current (32). The approach according to the invention is characterized in that, in the event of a cavity (44) being detected, a notification signal (52) is provided.