When the power mode is ON, the ECM sends authentication requests to the wireless access module via the CAN communication circuit. At this time, the wireless access module transmits response signals to the ECM via the CAN communication circuit. When response signals are received from the wireless access module, it is possible to start the engine. If it fails to receive the response signals from the wireless access module, the ECM sends authentication requests to the wireless access module again. If the wireless access module receives authentication requests from the ECM exceeding a predetermined number of times, the DTC is set.