An electronic control unit (ECU) and a vehicle control system are disclosed. When a vehicle ID rewrite instruction and a malfunction information erasure instruction are inputted to the system from an external scantool, one ECU in the system erases the malfunction information stored therein and determines whether the malfunction information stored in another ECU has been erased. When it is determined that the malfunction information stored in every ECU has been erased, the vehicle ID is rewritten. According to the above system, it is possible to prevent violation of a requirement, the requirement being such that when a vehicle ID is rewritten, malfunction information should be erased at the same time.