A circuit arrangement is proposed to diagnose a heating resistor, which is connected in series with a first switch, which connects the heating resistor to a power source for operation of the heating resistor with a heating current. Provision is made for means to operate the heating resistor with a diagnostic current during a cut-out time of the heating current and for means to acquire a diagnostic voltage as a measurement for the voltages occurring at the heating resistor as well as means to calculate the resistance of the heating resistor, which is taken as a basis for the diagnosis.