This refines the fatal major error code into a specific fault instance, the fatal counterpart to cardDiagNonFatalErrMinor. Paired with the fatal major code, this minor code often distinguishes between, say, a watchdog timeout during normal operation versus one during a firmware upgrade, which changes whether the fix is a hardware swap or a firmware rollback. For example, major code 7 with minor code 2 might specifically indicate the timeout occurred during an image download, pointing at a firmware issue rather than hardware.