A gate level, automated fault diagnosis scheme is proposed for scan-based BIST designs. The proposed scheme utilizes both fault capturing scan chain information and failing test vector information and enables location identification of single stuck-at faults to a neighborhood of a few gates through set operations on small pass/fail dictionaries. The proposed scheme is applicable to multiple stuck-at faults and bridging faults as well. The practical applicability of the suggested ideas is confirmed through numerous experimental runs on all three fault models.