The invention relates to a method for authenticating a vehicle (1) to a service unit (12) by means of a central processing unit (4) external to the vehicle. An initial value (Nr) is transmitted from the service unit (12) to the authentication unit (2) and, depending on the initial value (Nr), the authentication unit (2) reads a query command (6) from a query table (8) and sends it to a Interface (9) of the vehicle (1) output. The authentication unit (2) receives an output value (R) generated as a response from the interface (9) and calculates a vehicle test value (Hr) from the output value (R). The vehicle test value (Hr) and the initial value (Nr) are transmitted to the central processing unit (4). The central processing unit (4) reads a characteristic value (7) from a characteristic value table (11) as a function of the initial value (Nr) and calculates a further vehicle test value (Hr). If the vehicle test value (Hr) matches the further vehicle test value (Hr), the central processing unit sends a predetermined release signal to the service unit (12).
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