A steering drive system for a steering system of a transportation vehicle having a first control unit for actuating a first winding circuit of a steering drive motor with a test circuit to make available a defined changing test signal and a second control unit for actuating a second winding circuit of the steering drive motor, wherein a test signal reception circuit of the second control unit receives the test signal, and wherein the second control unit actuates the steering drive motor based on the presence or absence of the test signal.
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