Downtime associated with fault isolation impacts the performance of any system to a significant degree. Few repairmen are well versed in the art of troubleshooting and experienced repairmen are not always available and/or are very costly. A failure diagnostic expert system provides an effective method of failure diagnosis.

Diagnostic reasoning in expert systems is discussed with demonstrating methodologies by using a 1.6 liter, 1981 model Volkswagen Vanagon as an example. A procedure and methodology for building a diagnostic case base is demonstrated by building a Volkswagen Vanagon diagnostic case base. A significant diagnostic case base was developed in order to demonstrate and evaluate the appropriateness of CBR Express for failure diagnosis. CBR Express is a case-based matching application from Inference Corporation.