1. A method comprising: receiving system fault codes, component fault codes, and failure modes; generating a first level model comprising first level causal relationships and first level causal weights between the system fault codes and the component fault codes; generating a second level model comprising second level causal relationships and second level causal weights between the component fault codes and the failure modes; combining the first level model and the second level model to generate a graphical model; and determining, using the graphical model, one or more probability inferences.