A vehicle diagnosis system includes an electronic control unit, which executes a diagnosing process for determining whether any abnormality is present in a vehicle based on signals from vehicle devices. When any abnormality is detected, the electronic control unit stores in an EEPROM a diagnosis result indicative of the abnormality when a storage permission flag in the EEPROM is in the on-state. The storage permission flag is turned on from the off-state when receiving a storage permission command from an external unit. Thus, the storage of the diagnosis result into the EEPROM may be permitted at the time of transmitting the storage permission command externally to the ECU.