Robot systems have recently been studied for real world situations such as space exploration, underwater inspection, and disaster response. In extreme environments, a robot system has a probability of failure. Therefore, considering fault tolerance is important for mission success. In this study, we proposed a distributed cooperative fault diagnosis method for internal components of robot systems. This method uses diagnostic devices called diagnosers to observe the state of an electrical component. These diagnosers execute each diagnosis independently and in parallel with one another, and it is assumed that they are interconnected through wireless communication. A fault diagnosis technique was proposed that involves gathering the diagnosis results. Further, computer simulations confirmed that the distributed cooperative fault diagnosis method could detect component faults in simplified fault situations.