With the increasing of circuit density, the importance of locating open faults becomes larger. In recent years, built-in self test (BIST) is widely used to reduce test cost. Therefore, development of efficient fault diagnosis approach under BIST environment is much wanted. In this paper, we propose fanout-based fault diagnosis approach for open faults on pass/fail information. Experimental results for ISCAS'85 and ITC'99 benchmark circuits show that the number of candidate faults becomes less than 2 at most cases by using error path tracing and multiple stuck-at fault simulator.