Abstract: Disclosed is a vehicle diagnosis system including: a signal-collecting unit disposed at a proper place of the vehicle including CAN(Controller Area Network) communication modules which send a CAN signal to and receive it from a vehicle ECU for controlling states of all parts of the vehicle by a computer, through a CAN and which output an analog signal to a driver driven by the module according to a command from the vehicle ECU, wherein the signal-collecting unit synchronizes and collects the CAN signal and the analog signal at predetermined time intervals; and a diagnosing unit which detects changes of the CAN signal and the analog signal collected in the signal-collecting unit at synchronization collection periods, and if the change of any one of the two signals has not been detected, diagnoses that the CAN communication module outputting the relevant CAN signal and analog signal failed.