Importance

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Abstract

A self-diagnostic apparatus of vehicles which allows frozen diagnostic data to reflect correctly and efficiently a vehicle state upon the detection of an abnormality. A control unit has a CPU and a RAM which holds stored data even when the ignition key is turned off. The CPU detects an abnormality of individual on-board devices and when an abnormality of a device is detected, it stops updating diagnostic data and maintains data immediately prior to the detection of the abnormality. When updating of diagnosis data is not stopped, the contents of the RAM is updated at a predetermined updating period of time with diagnostic by data necessary for analyzing the device abnormality. The updating period becomes shorter as the rate of change of the diagnostic data grows larger. Through this, an adequate amount of diagnostic data near a time point at which the device abnormality occurs can be reliably and efficiently stored for later retrieval.

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First Claim