The invention relates to a computer-based diagnostic tester which can exchange information with the control devices installed in the motor vehicle using a diagnostic program via a diagnostic interface and via data lines. A method for improved checking of repairs is also presented with the diagnostic tester. The motor vehicle-mounted control devices have program routines for self-diagnostics of the control devices and are capable of storing identified faults in the form of fault codes in reserved memory areas. The diagnostic program which is implemented in the diagnostic tester reads the fault codes out from the reserved memory areas, interprets the fault codes and displays them on a display together with the interpretations. In order to check to what extent repairs which have been performed have been successfully concluded, status polling is carried out using the diagnostic program implemented in the diagnostic tester. During this status polling, the status information of all the fault codes known in the system is interrogated and evaluated. In the process, all the fault codes whose fault setting conditions have either been tested positively or whose test requirements were not present in order to be able to carry out a test are displayed. The fault codes which are to be displayed are firstly stored here in one or more primary first fault memories, read out and then copied into a secondary, second fault memory. This permits the use of the total reset of the primary fault memories which is prescribed in the USA for diagnostic systems without information which is relevant to the checking of repairs in the second fault memory being lost.