Diagnostic device for a multi-voltage vehicle electrical system, a multi-voltage vehicle electrical system, and a method for operating a multi-voltage vehicle electrical system

A diagnostic device for a multi-voltage electrical system of a motor vehicle having an internal combustion engine, the multi-voltage vehicle electrical system including a first subnetwork acted on by a first voltage and at least one other subnetwork acted on by at least one other voltage, the first voltage being higher than the at least one other voltage, and the first subnetwork and the at least one other subnetwork having a shared first ground connection, the diagnostic device comprising:

• at least one second ground connection;
• a measuring unit configured to measure a current flow via the at least one second ground connection;
• and
• a diagnostic unit configured to diagnose a disturbance in at least one of the shared first ground connection and the at least one second ground connection on the basis of the measured current flow via the at least one second ground connection as a function of at least one operating state of the multi-voltage vehicle electrical system, wherein the at least one second ground connection and the shared first ground connection are connected in parallel such that currents flowing via a starter situated in the second subnetwork and a generator situated in the first subnetwork flow via the shared first ground connection and the at least one second ground connection when the internal combustion engine is started under the conditions of the shared first ground connection being undisrupted and the at least one second ground connection being undisrupted.

A multi-voltage electrical system for a motor vehicle, comprising:

• a first subnetwork acted on by a first voltage;
• at least one other subnetwork acted on by at least one other voltage, wherein the first voltage is higher than the at least one other voltage, and the first subnetwork and the at least one other subnetwork have a shared first ground connection;
• and
• a diagnostic device including:
• at least one second ground connection;
• a measuring unit configured to measure a current flow via the at least one second ground connection;
• and
• a diagnostic unit configured to diagnose a disturbance in at least one of the shared first ground connection and the at least one second ground connection on the basis of the measured current flow via the at least one second ground connection as a function of at least one operating state of the multi-voltage vehicle electrical system, wherein the at least one second ground connection and the shared first ground connection are connected in parallel such that currents flowing via a starter situated in the second subnetwork and a generator situated in the first subnetwork flow via the shared first ground connection and the at least one second ground connection when the internal combustion engine is started under the conditions of the shared first ground connection being undisrupted and the at least one second ground connection being undisrupted.