A vehicle control system comprising: a plurality of sensors; a central control device configured to calculate target outputs of a plurality of actuators, based on outputs of the respective sensors; and a plurality of relay devices each disposed in a communication path between the central control device and a corresponding actuator among the actuators and configured to relay a control signal generated by the central control device, wherein the actuators include a specific actuator related to driving control, braking control, or steering control of a vehicle, the plurality of relay devices include a specific relay device capable of communicating with the specific actuator, the central control device includes a central abnormality diagnosis unit configured to diagnose an abnormality in the central control device, the specific relay device among the plurality of relay devices includes a specific abnormality diagnosis unit configured to diagnose an abnormality in the specific relay device, and a backup calculation unit capable of calculating a target output of the specific actuator coupled to the specific relay device, the specific relay device is configured to receive an output of at least one sensor among the sensors, and in response to the central abnormality diagnosis unit detecting an abnormality in the central control device, the backup calculation unit of the specific relay device controls the specific actuator, based on information obtained by the sensor and input to the specific relay device, characterized in that a relay device other than the specific relay device among the plurality of relay devices does not have a self-diagnosis function, and the specific relay device includes a communication diagnosis unit configured to diagnose an abnormality in a state of communication between the specific relay device and the central control device, and in response to the communication diagnosis unit detecting an abnormality in the state of communication between the specific relay device and the central control device, the backup calculation unit of the specific relay device controls the specific actuator, based on information obtained by the sensor and input to the specific relay device. a plurality of sensors; a central control device configured to calculate target outputs of a plurality of actuators, based on outputs of the respective sensors; and a plurality of relay devices each disposed in a communication path between the central control device and a corresponding actuator among the actuators and configured to relay a control signal generated by the central control device, wherein the actuators include a specific actuator related to driving control, braking control, or steering control of a vehicle, the plurality of relay devices include a specific relay device capable of communicating with the specific actuator, the central control device includes a central abnormality diagnosis unit configured to diagnose an abnormality in the central control device, the specific relay device among the plurality of relay devices includes a specific abnormality diagnosis unit configured to diagnose an abnormality in the specific relay device, and a backup calculation unit capable of calculating a target output of the specific actuator coupled to the specific relay device, the specific relay device is configured to receive an output of at least one sensor among the sensors, and in response to the central abnormality diagnosis unit detecting an abnormality in the central control device, the backup calculation unit of the specific relay device controls the specific actuator, based on information obtained by the sensor and input to the specific relay device, characterized in that a relay device other than the specific relay device among the plurality of relay devices does not have a self-diagnosis function, and the specific relay device includes a communication diagnosis unit configured to diagnose an abnormality in a state of communication between the specific relay device and the central control device, and in response to the communication diagnosis unit detecting an abnormality in the state of communication between the specific relay device and the central control device, the backup calculation unit of the specific relay device controls the specific actuator, based on information obtained by the sensor and input to the specific relay device.