Abstract: A device (1) for determining whether a maintenance message generated during an operating cycle of a system by a maintenance device (2) monitoring the system is or is not representative of a real fault in the system. The device (1) includes a comparator (D) which compares a short-term occurrence rate of the message to a long-term occurrence rate of the message, for each maintenance message generated, and determining whether the message is or is not representative of a real fault. The occurrence rates are calculated by a computer (CAL) on the basis of information contained in memories (M1, M2, MN) and indicate the presence or non-presence of the message in the course of predicting cycles.