Radio-based vehicle access system having - a data bus system having - a master module with a master bus transceiver , and - at least a first slave module and a structurally identical second slave module , which are arranged in a daisy-chain configuration with the master module , - wherein the first slave module has a discrete bus activation circuit with a first switching element which is connected, on the input side, to a first slave bus transceiver and, via the latter, to a first microcontroller of the first slave module and is connected, on the output side, to a second slave bus transceiver of the second slave module , and wherein the first switching element can be controlled to selectively connect and disconnect the second slave bus transceiver to/from the master bus transceiver by means of a voltage signal from the first microcontroller , also having - a control device for selectively unlocking and locking vehicle doors, which is connected to the data bus system , wherein the master module is an integrative part of the control device , wherein vehicle doors are connected to the data bus system insofar as the vehicle doors are connected to the control device of the data bus system for the selective unlocking and locking of the vehicle doors by means of the control device, - wherein the slave modules (122a-122d) of the data bus system , which are connected to the control device via the data bus system , also each have a radio transceiver (123a-123d) which is connected via the data bus system and is intended to transmit and receive in order to exchange a coding key with a radio-based vehicle key outside the vehicle, wherein the coding key is provided for the selective unlocking and locking of vehicle doors by way of the control device. - a data bus system having - a master module with a master bus transceiver , and - at least a first slave module and a structurally identical second slave module , which are arranged in a daisy-chain configuration with the master module , - wherein the first slave module has a discrete bus activation circuit with a first switching element which is connected, on the input side, to a first slave bus transceiver and, via the latter, to a first microcontroller of the first slave module and is connected, on the output side, to a second slave bus transceiver of the second slave module , and wherein the first switching element can be controlled to selectively connect and disconnect the second slave bus transceiver to/from the master bus transceiver by means of a voltage signal from the first microcontroller , also having - a control device for selectively unlocking and locking vehicle doors, which is connected to the data bus system , wherein the master module is an integrative part of the control device , wherein vehicle doors are connected to the data bus system insofar as the vehicle doors are connected to the control device of the data bus system for the selective unlocking and locking of the vehicle doors by means of the control device, - wherein the slave modules (122a-122d) of the data bus system , which are connected to the control device via the data bus system , also each have a radio transceiver (123a-123d) which is connected via the data bus system and is intended to transmit and receive in order to exchange a coding key with a radio-based vehicle key outside the vehicle, <EOS>