Abstract: By the utilization of the visual tool Borland C ++ Builder in Windows and BP network, a fault diagnosis system was designed. Combining the fault diagnosis module with the monitoring module by using the multi thread technique, a fault diagnosis system for electronic control diesel engine was achieved. The results obtained from the engine bench test indicated that some common faults of diesel could be diagnosed and the system was reliable. It was also proved that the involvement of NN technique in the system to implement fault diagnosis for the electronic control discel engines is feasible.