With the development of wireless mesh networks (WMNs), fault diagnosis in WMNs is becoming a very challenging task. In this paper, a two-level scheme for fault diagnosis in WMNs is presented. We partition the network into a two-level topology architecture where level 1 is composed of mesh clients and level 2 consists of mesh routers. A new comparison approach is introduced to diagnose the two levels. On the basis of the new comparison approach, every node in WMNs can be diagnosed either as fault-free or faulty. Our protocol assumes that the WMN's topology may change during the testing phase and utilize the shortest path spanning tree, which is constructed along with the process of fault diagnosis, to disseminate local messages and global messages in WMNs. The proposed model is only for static fault circumstances. We provide the analysis of correctness, communication complexity, and time complexity of our protocol, and the comparison between our protocol and others through both theoretical proof and practical simulation. The analysis shows that our model has significant advantages over other existing models. Copyright © 2012 John Wiley & Sons, Ltd.