Disclosed in the present invention is an apparatus and method for diagnosing bypass valve failure. The apparatus and method for diagnosing bypass valve failure according to the present invention are characterized by comprising: an electric supercharger which comprises a motor and an electric compressor which is actuated by means of the motor so as to supply supercharged air to the combustion chamber of the engine; a bypass valve provided on a bypass line which branches from the intake line where the electric supercharger is provided, and which joins same at the frontend of a throttle valve which adjusts the intake amount supplied to the combustion chamber; a vehicle-state input unit into which vehicle-state information is input; and a control unit which receives input of the vehicle-state from the vehicle-state input unit and determines whether the failure diagnosis of a bypass valve start conditions are satisfied, and, if the failure diagnosis of a bypass valve start conditions are satisfied, transmits 'open' or 'close' control instructions to the bypass valve and transmits, to the electric supercharger, a specific rotational-speed target value for determining whether the bypass valve is in the normal open state or the normal closed state, so as to determine whether the bypass valve is subject to stuck-open failure or stuck-closed failure.
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