A system for diagnosing an abnormality of one or more main control units, the system comprising: one or more battery management modules, which are connected to one or more batteries, respectively; an auxiliary control unit configured to diagnose the abnormality of one or more main control units; and an interface integrated circuit configured to perform communication between the one or more main control units, the auxiliary control unit, and the one or more battery management modules, characterized in that the one or more main control units are configured to set a reference voltage value for diagnosing overvoltage or low-voltage abnormality of one or more batteries, the one or more main control units are configured to change the preset reference voltage value such that overvoltage or low-voltage abnormality is diagnosed in one or more batteries, and the auxiliary control unit is configured to check whether a fault generation signal is output from one or more battery management modules, wherein, if the fault generation signal is output from one or more battery management modules, the auxiliary control unit diagnoses that the one or more main control units are in a functional safety state and transmit the fault generation signal received from one or more battery management modules to the one more main control units, wherein the one or more main control units reset the value of the changed reference value to the initially set reference voltage value and if the state of the one or more batteries is diagnosed by changing the value of the preset reference value, but all of the batteries are diagnosed to have neither overvoltage nor undervoltage and the fault generation signal is not output, the auxiliary control unit diagnoses that an abnormality is generated in the one or more main control units. one or more battery management modules, which are connected to one or more batteries, respectively; an auxiliary control unit configured to diagnose the abnormality of one or more main control units; and an interface integrated circuit configured to perform communication between the one or more main control units, the auxiliary control unit, and the one or more battery management modules, characterized in that the one or more main control units are configured to set a reference voltage value for diagnosing overvoltage or low-voltage abnormality of one or more batteries, the one or more main control units are configured to change the preset reference voltage value such that overvoltage or low-voltage abnormality is diagnosed in one or more batteries, and the auxiliary control unit is configured to check whether a fault generation signal is output from one or more battery management modules, wherein, if the fault generation signal is output from one or more battery management modules, the auxiliary control unit diagnoses that the one or more main control units are in a functional safety state and transmit the fault generation signal received from one or more battery management modules to the one more main control units, wherein the one or more main control units reset the value of the changed reference value to the initially set reference voltage value and if the state of the one or more batteries is diagnosed by changing the value of the preset reference value, but all of the batteries are diagnosed to have neither overvoltage nor undervoltage and the fault generation signal is not output, the auxiliary control unit diagnoses that an abnormality is generated in the one or more main control units.