Method for triggering a function of a motor vehicle by means of a passive access system, wherein the passive access system comprises: - a control device on the motor vehicle side, which is coupled to at least one first RF transmitting and receiving station and a second RF transmitting and receiving station, which are positioned at a distance from each other on the motor vehicle, - an ID transponder with a microcontroller and with an RF transmitting and receiving circuit of the ID transponder controlled by the microcontroller for communication with the control device on the motor vehicle side; wherein, before the function is triggered, the control device and the ID transmitter carry out an authentication process among themselves to check whether the ID transmitter is an ID transmitter authorized to trigger said function, wherein the authentication process comprises the following steps for each of the first RF transmitting and receiving station and the second RF transmitting and receiving station: a) Transmitting an RF signal (8, 8') on the motor vehicle side with a respective predetermined transmission signal strength S_KFZ from the RF transmitting and receiving station (3, 4), the RF signal being received by the ID transmitter, b) Transmitting an RF signal (9, 9') on the ID transmitter side with a predetermined transmission signal strength S_ID to the RF transmitting and receiving station, the RF signal being received by the RF transmitting and receiving station (3, 4), c) Detecting a received signal strength E_KFZ of the RF signals (8, 8') on the vehicle side at the position of the ID transmitter and transmitting the received signal strength E_KFZ to the control device on the vehicle side, d) Detecting a received signal strength E_ID of the RF signal (9, 9') on the ID transmitter side at the RF transmitting and receiving station (3, 4) and transmitting the received signal strengths to the control device on the motor vehicle side, e) Comparing a signal attenuation of the vehicle-side RF signal (8, 8') from the RF transmitting and receiving stations with the signal attenuation of the associated ID transmitter-side RF signal (9, 9') received there. - a control device on the motor vehicle side, which is coupled to at least one first RF transmitting and receiving station and a second RF transmitting and receiving station, which are positioned at a distance from each other on the motor vehicle, - an ID transponder with a microcontroller and with an RF transmitting and receiving circuit of the ID transponder controlled by the microcontroller for communication with the control device on the motor vehicle side; a) Transmitting an RF signal (8, 8') on the motor vehicle side with a respective predetermined transmission signal strength S_KFZ from the RF transmitting and receiving station (3, 4), the RF signal being received by the ID transmitter, b) Transmitting an RF signal (9, 9') on the ID transmitter side with a predetermined transmission signal strength S_ID to the RF transmitting and receiving station, the RF signal being received by the RF transmitting and receiving station (3, 4), c) Detecting a received signal strength E_KFZ of the RF signals (8, 8') on the vehicle side at the position of the ID transmitter and transmitting the received signal strength E_KFZ to the control device on the vehicle side, d) Detecting a received signal strength E_ID of the RF signal (9, 9') on the ID transmitter side at the RF transmitting and receiving station (3, 4) and transmitting the received signal strengths to the control device on the motor vehicle side, e) Comparing a signal attenuation of the vehicle-side RF signal (8, 8') from the RF transmitting and receiving stations with the signal attenuation of the associated ID transmitter-side RF signal (9, 9') received there.