DIAGNOSTIC METHOD

PURPOSE:To eliminate the necessity of so many information transmission lines for transferring diagnostic results, by making a diagnosed result of a central controller to be diagnosed compare with a normal result received from a diagnosing central controller, and transmit the compared result to the diagnosing central controller. CONSTITUTION:When the diagnosing central controller CC0 checks the normarity of the central controller CC1 to be diagnosed, a diagnostic program DP and the normal result are stored in a main memory MM1. When the controller CC0 sends a starting signal ST to the controller CC1, the controller CC1 compares the diagnosed result data DD obtained by executing a diagnosis based upon the program DP stored in the MM1 with the normal result stored in the MM1, and sends an interruption signal IR0 to the controller CC0 when both results coincide with each other, and sends an interruption signal IR1 at the time of inconsistency. In accordance with the interruption signal IR0 or IR1 received by the controller CC0, the normality of the controller CC1 can be discriminated collectively.