Counterfactual Fault Responsibility in a Dynamic Structural Causal Model of a DC Motor (Short Paper)

Abstract

Model-based diagnosis can identify fault hypotheses that are compatible with observed abnormal behaviour. Still, it does not necessarily determine which fault is responsible for a particular symptom when several faults are active simultaneously. We propose a counterfactual framework for post-diagnostic fault responsibility analysis in dynamical systems. The physical process is represented as a time-indexed structural causal model, while faults are encoded as interventions on individual system mechanisms. Responsibility is evaluated by comparing the factual system trajectory with counterfactual trajectories in which candidate faults are removed while the operating conditions and control structure are kept fixed. We instantiate the framework on an electro-thermo-mechanical model of a DC motor and evaluate it in two simulated multi-fault scenarios. The results show that counterfactual fault removal can separate the contributions of different faults to individual symptoms and distinguish severity contribution from necessity for a failure event. The proposed approach therefore complements conventional diagnosis with symptom-level causal explanations of faulty system behaviour.