A vehicle diagnosing system for performing a fault diagnosis of a vehicle including an idling stop control system, the idling stop control system executing an idling stop for stopping a drive source of the vehicle from idling by cooperatively controlling a plurality of electronic control units (20, 22, 24, 26, 28, 30, 32, 34, 36), wherein the vehicle comprises: a plurality of warning lamps (104, 106, 120, 122, 124, 126, 150, 152, 154, 156, 158, 160, 162) each configured to light when a fault has occurred within a target range controlled by specific ones of the electronic control units (20, 22, 24, 26, 28, 30, 32, 34, 36), and demand an inspection or repair of the failure; and an idling stop controller configured to automatically execute the idling stop when a predetermined condition is satisfied; wherein when the electronic control units (20, 22, 24, 26, 28, 30, 32, 34, 36) detect a fault in the target ranges controlled thereby, the electronic control units (20, 22, 24, 26, 28, 30, 32, 34, 36) record fault codes; the fault codes include idling stop fault codes defined as inhibiting the idling stop of the drive source, and non-idling stop fault codes not defined as inhibiting the idling stop; the idling stop fault codes include first idling stop fault codes defined as energizing the warning lamps (104, 106, 120, 122, 124, 126, 150, 152, 154, 156, 158, 160, 162) and second idling stop fault codes not defined as energizing the warning lamps (104, 106, 120, 122, 124, 126, 150, 152, 154, 156, 158, 160, 162); the vehicle further comprises an idling stop failure indicator configured to indicate an idling stop fault corresponding to one of the second idling stop fault codes when the idling stop fault which records the one of the second idling stop fault codes in any of the electronic control units (20, 22, 24, 26, 28, 30, 32, 34, 36) has occurred in a target range controlled thereby; the idling stop failure indicator includes a single indicator lamp, and the idling stop failure indicator indicates the idling stop fault by the single indicator lamp when the idling stop fault which records the one of the second idling stop fault codes in any of the electronic control units (20, 22, 24, 26, 28, 30, 32, 34, 36) has occurred in the target range controlled thereby. a plurality of warning lamps (104, 106, 120, 122, 124, 126, 150, 152, 154, 156, 158, 160, 162) each configured to light when a fault has occurred within a target range controlled by specific ones of the electronic control units (20, 22, 24, 26, 28, 30, 32, 34, 36), and demand an inspection or repair of the failure; and an idling stop controller configured to automatically execute the idling stop when a predetermined condition is satisfied; wherein when the electronic control units (20, 22, 24, 26, 28, 30, 32, 34, 36) detect a fault in the target ranges controlled thereby, the electronic control units (20, 22, 24, 26, 28, 30, 32, 34, 36) record fault codes; the fault codes include idling stop fault codes defined as inhibiting the idling stop of the drive source, and non-idling stop fault codes not defined as inhibiting the idling stop; the idling stop fault codes include first idling stop fault codes defined as energizing the warning lamps (104, 106, 120, 122, 124, 126, 150, 152, 154, 156, 158, 160, 162) and second idling stop fault codes not defined as energizing the warning lamps (104, 106, 120, 122, 124, 126, 150, 152, 154, 156, 158, 160, 162); the vehicle further comprises an idling stop failure indicator configured to indicate an idling stop fault corresponding to one of the second idling stop fault codes when the idling stop fault which records the one of the second idling stop fault codes in any of the electronic control units (20, 22, 24, 26, 28, 30, 32, 34, 36) has occurred in a target range controlled thereby; the idling stop failure indicator includes a single indicator lamp, and the idling stop failure indicator indicates the idling stop fault by the single indicator lamp when the idling stop fault which records the one of the second idling stop fault codes in any of the electronic control units (20, 22, 24, 26, 28, 30, 32, 34, 36) has occurred in the target range controlled thereby.