On-vehicle controller failure diagnosing method and apparatus

Abstract

Even if a power source is cut OFF while a failure is present and then the power source is turned back ON with the failure uncorrected, the details of the same failure will not be recorded as failure history data, thus permitting correct failure history data to be stored. In an on-vehicle controller failure diagnosing method in which, if a vehicle failure happens, the time at which the failure happened and the details of the failure are stored as failure history data, the details of a detected failure are stored as failure history data only if the details of the failure which existed when the power source of the on-vehicle controller was cut OFF are different from the details of the failure detected during a failure diagnosis carried out when the power source is turned back ON. Further, it is determined, during the failure diagnosis carried out after the power source of the on-vehicle controller is turned ON, whether the cause of a failure which existed when the power source was cut OFF has been eliminated, and if the cause is found to be eliminated, then it is determined that the failure which existed when the power source was cut OFF has been completely corrected, and the result is stored as failure history data.