A method for modifying a control unit of an autonomous car , the autonomous car being equipped with basic sensors adapted for recording sensor data based on which a fusion model of objects and an environment surrounding the autonomous car can be generated, wherein the sensor data recorded by the basic sensors enables the control unit to control the autonomous car in autonomous driving mode, the method comprising the steps of - while the control unit is in a first state, recording the sensor data by the basic sensors during an autonomous test action performed in autonomous driving mode of the autonomous car , - in response to being triggered by a disengagement event, logging disengagement related data comprising the sensor data recorded by the basic sensors in an analysis time window before the disengagement event (S40), - generating a virtual scenario in a simulator apparatus for the analysis time window based on the disengagement related data, characterized in that the virtual scenario comprises a virtual counterpart of the autonomous car having virtual counterparts of the basic sensors, and performing a first virtual autonomous run according to the autonomous test action with the virtual counterpart of the autonomous car using the first state of the control unit in the simulator apparatus, so that the first virtual autonomous run leads to the disengagement event in the virtual scenario (S50), and the method further comprising the steps of - identifying based on the virtual scenario an inadequately operating component of the control unit, wherein the disengagement event has been caused by inadequate operation of the inadequately operating component of the control unit (S60), and - generating a second state of the control unit based on the first state of the control unit by modifying the inadequately operating component of the control unit, performing a second virtual autonomous run according to the autonomous test action with the virtual counterpart of the autonomous car using the second state of the control unit in the simulator apparatus (S70), checking whether the disengagement event is avoided in the second virtual autonomous run, and storing the modified component of the control unit if the disengagement event is avoided in the second virtual autonomous run. - while the control unit is in a first state, recording the sensor data by the basic sensors during an autonomous test action performed in autonomous driving mode of the autonomous car , - in response to being triggered by a disengagement event, logging disengagement related data comprising the sensor data recorded by the basic sensors in an analysis time window before the disengagement event (S40), - generating a virtual scenario in a simulator apparatus for the analysis time window based on the disengagement related data, - identifying based on the virtual scenario an inadequately operating component of the control unit, wherein the disengagement event has been caused by inadequate operation of the inadequately operating component of the control unit (S60), and - generating a second state of the control unit based on the first state of the control unit by modifying the inadequately operating component of the control unit, performing a second virtual autonomous run according to the autonomous test action with the virtual counterpart of the autonomous car using the second state of the control unit in the simulator apparatus (S70), checking whether the disengagement event is avoided in the second virtual autonomous run, and storing the modified component of the control unit if the disengagement event is avoided in the second virtual autonomous run. <EOS>