Motor vehicle control unit with redundant power supply, and corresponding motor vehicle

A control unit for a motor vehicle, having at least one supply connection for receiving a supply voltage from a respective supply line needing to be secured against a predetermined electrical reaction from the control unit, wherein the at least one supply connection is connected via a respective current path to a circuit input of an electrical device circuit of the control unit, and to protect against the reaction there is provision for, in the respective current path of the at least one supply connection, a respective unidirectional first blocking element that provides for a unidirectionally directed flow of current to the device circuit and a blocking effect for a flow of current to the respective supply connection, wherein a diagnostic circuit is configured to check the blocking effect by a predetermined diagnostic routine, wherein a second unidirectional blocking element is respectively connected in series with the first blocking element in the respective current path of the at least one supply connection, wherein the second blocking element likewise provides for the unidirectional flow of current to the device circuit, and the diagnostic circuit is configured to use the diagnostic routine to also check the blocking effect of the second blocking element.