The aim of the invention is to improve the diagnosis of motor vehicle systems comprising a plurality of functional components in a network. To this end, the individual status data of the control units (11, 12, 13, 14) is monitored in a central diagnostic control unit (15) using a mathematical model. Each control unit can also be provided with a self-diagnosis optionally based on a model. By calculating error or causes of error using a model, the control units do not need to be provided with large databases for the diagnosis of error.