In a circuit arrangement (10a) for operating an injector arrangement (12a) for injecting fuel in an internal combustion engine of a motor vehicle, in order to obtain information easily as to the degree to which each valve is open when the injector arrangement is in operation, a measuring signal (S0) is superposed on a control voltage that is supplied to an actuator (Cpiezo, Rpiezo) and, based on an evaluation of the electrical properties of the actuator (Cpiezo, Rpiezo), a detection signal (S2) is produced that is representative of the position of the valve body (44a) relative to the valve seat (46a).