A method for operating a rotational speed sensor (1a.i; 1b.i) comprising a sensor element (5.i; 3.i) in a vehicle, in particular a utility vehicle, wherein the sensor element (5.i; 3.i) interacts with a pole wheel (4.i) on a wheel (2.i) of the vehicle and an effective parameter (UW.i; IW.i) generated by the interaction of the pole wheel (4.i) with the sensor element (5.i; 3.i) is evaluated in the form of a measurand (U.i; I.i) in an evaluation module and, depending on the measurand (U.i; I.i), an output variable (UK.i, SK.i) characterizing the rotational speed (D.i) of the wheel (2.i) is output, wherein the sensor element (5.i; 3.i) is supplied via the evaluation module with a sensor voltage (Usens) influencing the measurand (U.i, I.i), wherein the functionality of the evaluation module is monitored by a redundancy module independent from the evaluation module as to whether the sensor element (5.i; 3.i) is supplied or can be supplied with the sensor voltage (Usens) by the evaluation module, wherein in the event of a malfunction of the evaluation module, as a consequence thereof the sensor element (5.i; 3.i) is or can no longer be supplied with the sensor voltage (Usens) by the evaluation module, a redundancy sensor voltage (Usens_r) is provided by the redundancy module, with which the respective sensor element (5.i; 3.i) is supplied instead to form a redundant voltage supply of the sensor element (5.i; 3.i), wherein in the redundancy module at least the following steps are performed to monitor the functionality of the evaluation module: - detecting a redundancy measurand (Ur.i; Ir.i) ensuing in the redundancy module, wherein the redundancy measurand (Ur.i; Ir.i) arises on the basis of the interaction of the pol wheel with the sensor element (5.i; 3.i), which is supplied with the sensor voltage (Usens) specified by the evaluation module; and - determining whether the redundancy measurand (Ur.i; Ir.i) is an indication that a sensor voltage (Usens) is present which corresponds to a ground potential within a fault tolerance, characterized in that, in the presence of a redundancy measurand (Ur.i; Ir.i) that indicates a sensor voltage (Usens) which corresponds to a ground potential within the fault tolerance, a malfunction of the evaluation module is inferred, as a consequence whereof the sensor element (5.i; 3.i) is or can no longer be supplied with the sensor voltage (Usens) by the evaluation module, only when a redundancy measurand (Ur.i; Ir.i), which is assigned to at least one further sensor element (5.i; 3.i) of at least one further rotational speed sensor (1a.i; 1b.i) of the same sensor arrangement likewise indicates a sensor voltage (Usens), which corresponds to a ground potential within the fault tolerance, wherein the at least one further sensor element (5.i; 3.i) is likewise supplied with the sensor voltage (Usens) by the same evaluation module and is likewise monitored for a malfunction by the redundancy module. - detecting a redundancy measurand (Ur.i; Ir.i) ensuing in the redundancy module, wherein the redundancy measurand (Ur.i; Ir.i) arises on the basis of the interaction of the pol wheel with the sensor element (5.i; 3.i), which is supplied with the sensor voltage (Usens) specified by the evaluation module; and - determining whether the redundancy measurand (Ur.i; Ir.i) is an indication that a sensor voltage (Usens) is present which corresponds to a ground potential within a fault tolerance, in the presence of a redundancy measurand (Ur.i; Ir.i) that indicates a sensor voltage (Usens) which corresponds to a ground potential within the fault tolerance, a malfunction of the evaluation module is inferred, as a consequence whereof the sensor element (5.i; 3.i) is or can no longer be supplied with the sensor voltage (Usens) by the evaluation module, only when a redundancy measurand (Ur.i; Ir.i), which is assigned to at least one further sensor element (5.i; 3.i) of at least one further rotational speed sensor (1a.i; 1b.i) of the same sensor arrangement likewise indicates a sensor voltage (Usens), which corresponds to a ground potential within the fault tolerance, wherein the at least one further sensor element (5.i; 3.i) is likewise supplied with the sensor voltage (Usens) by the same evaluation module and is likewise monitored for a malfunction by the redundancy module.