Abstract: A diagnostic system for control apparatus of a motor vehicle equipped with self-diagnostic functions in which the control apparatus are connected with each other by way of a diagnostic bus and a defect lamp line. Diagnostic functions can be initiated by way of a key or momentary switch in an initialization line of the diagnostic bus whereby the diagnostic results can be read out at a defect lamp connected to the defect lamp line by way of flashing code word. The defect output thereby takes place strictly sequentially, defect-by-defect and control apparatus by control apparatus. In order to be able to discontinue at any time a diagnostic analysis of the control apparatus and to be able to continue to the diagnostic analysis of the next control apparatus, a newly defined special signal emission is applied to the initialization line.