17. A method comprising: receiving system diagnostic trouble codes (DTCs), component DTCs, and root causes; determining a first level model comprising first level causal relationships and first level causal weights between system DTCs and component DTCs; determining a second level model comprising second level causal relationships and second level causal weights between component DTCs and root causes; and generating an acyclic graphical model based on the first level model and the second level model.
17. A method comprising: receiving system diagnostic trouble codes (DTCs), component DTCs, and root causes; determining a first level model comprising first level causal relationships and first level causal weights between system DTCs and component DTCs; determining a second level model comprising second level causal relationships and second level causal weights between component DTCs and root causes; and generating an acyclic graphical model based on the first level model and the second level model. 20. The method of claim 17 , wherein: the first level causal weights comprise conditional probabilities of system DTCs given component DTCs; and the second level causal weights comprise conditional probabilities of component DTCs given root causes.