A data bus system of a motor vehicle includes at least one first and one second control device which communicates with each another via at least one data bus. In order to be able to localize errors more easily, the system has at least one identification device which provides an identifier to each of the messages sent by the first and the second control device. The first control device receives a first message, and the identification device causes the first control device to provide the message sent therefrom with a first identifier. The second control device receives the message sent by the first control device with the first identifier, and the identification device causes the second control device to provide the message sent therefrom with a second identifier.