A control unit 1 has a CPU 101 and a backup RAM 102. The CPU 101 detects diagnostic data necessary for analyzing malfunctions of instruments installed in a motor vehicle, and updates and stores the data in sequence in the backup RAM 102 so that when malfunctions are detected, the CPU 101 inhibits updating...http://www.google.de/patents/US5506773?utm_source=gb-gplus-sharePatent US5506773 - Self-diagnosing apparatus for motor vehicles