A device for aiding the location of a failure within a complex system may include a database that stores diagnostic aid rules; a detector that detects a failure, if any, of the complex system and provides, upon a failure, information relating to the origin of this failure; and a central unit that determines, for any failure detected, on the basis of the diagnostic aid rules and the failure origination information, the element or elements of the complex system that may have caused the failure. Additionally, the central unit determines the corresponding probability that each element caused the failure for presentation to a user.