- Abstract With increasing deployment of multi-agent and distributed systems, there is an increasing need for failure diagnosis systems. While successfully tackling key challenges in multiagent settings, model-based diagnosis has left open the diagnosis of coordination failures, where failures often lie in the boundaries between agents, and thus the inputs to the model—with which the diagnoser simulates the system to detect discrepancies—are not known. However, it is possible to diagnose such failures using a model of the coordination between agents. This paper formalizes model-based coordination diagnosis, using two coordination primitives (concurrence and mutual exclusion). We define the consistencybased and abductive diagnosis problems within this formalization, and show that both are NP-Hard by mapping them to other known problems.