Method for enabling the exchange of data between a central data processing device, which is connected or can be connected to a network, and a second data processing unit in a motor vehicle, which is configured for wireless connection to the network, having the steps of: - providing a portable device, in which an electronic identifier is stored, which can be output, - providing a device for coupling the portable device to the motor vehicle, wherein, when coupling the portable device to the motor vehicle, the electronic identifier can be output and transmitted to the second data processing unit, - providing or making use of the possibility of setting up at least one user account in the second data processing unit, - providing the central data processing unit, which is coupled to the network and in which user accounts are managed, - coupling the portable device to the motor vehicle, - providing a link to a predetermined user account of the central data processing device on a predetermined user account, which is provided or configured for this purpose in the second data processing unit, in which the electronic identifier is stored on the second data processing unit and is associated at that location with the predetermined user account, and in which it is ensured that the electronic identifier is stored on the central data processing device and is associated at that location with the predetermined user account, - generating a connection of the second data processing unit to the central data processing device via the network, - transmitting data on the user account of the central data processing device to the second data processing unit and/or transmitting data on the predetermined user account of the second data processing unit to the linked predetermined user account of the central data processing device, characterised in that - a user name and a password and/or other input data are associated with user accounts on the central data processing device as input data in each case, and in that the providing of a link after the portable device has been coupled to the motor vehicle is carried out by a connection of the second data processing unit to the central data processing device being produced via the network and, when the device is coupled to the motor vehicle, input data are entered, in that it is verified in the central data processing device, whether the input data, which have been entered, are correct, and in that, if the input data have been correctly entered, the electronic identifier of the portable device, which is coupled to the motor vehicle, is stored on a user account on the second data processing unit together with connection data to the predetermined user account on the central data processing unit. - providing a portable device, in which an electronic identifier is stored, which can be output, - providing a device for coupling the portable device to the motor vehicle, wherein, when coupling the portable device to the motor vehicle, the electronic identifier can be output and transmitted to the second data processing unit, - providing or making use of the possibility of setting up at least one user account in the second data processing unit, - providing the central data processing unit, which is coupled to the network and in which user accounts are managed, - coupling the portable device to the motor vehicle, - providing a link to a predetermined user account of the central data processing device on a predetermined user account, which is provided or configured for this purpose in the second data processing unit, in which the electronic identifier is stored on the second data processing unit and is associated at that location with the predetermined user account, and in which it is ensured that the electronic identifier is stored on the central data processing device and is associated at that location with the predetermined user account, - generating a connection of the second data processing unit to the central data processing device via the network, - transmitting data on the user account of the central data processing device to the second data processing unit and/or transmitting data on the predetermined user account of the second data processing unit to the linked predetermined user account of the central data processing device, - a user name and a password and/or other input data are associated with user accounts on the central data processing device as input data in each case, and in that the providing of a link after the portable device has been coupled to the motor vehicle is carried out by a connection of the second data processing unit to the central data processing device being produced via the network and, when the device is coupled to the motor vehicle, input data are entered, in that it is verified in the central data processing device, whether the input data, which have been entered, are correct, and in that, if the input data have been correctly entered, the electronic identifier of the portable device, which is coupled to the motor vehicle, is stored on a user account on the second data processing unit together with connection data to the predetermined user account on the central data processing unit.