I'm not sure if I understand what you mean, but this is not a software thing. The LED stops blinking when I unplug RX/TX. This means the sensor stops its detection process. 

Any news?

Additionally: the sensor does automatically start after power-on, but only when the serial port is connected. This tells me the “sensorCfgStart 1” is doing something, but it somehow relies on the serial port connection.

Thank you for your suggestion. I've tried to use both “sensorCfgStart 1” and sensorCfgStart 1m", and save the configuration using “saveCfg 0x45670123 0xCDEF89AB 0x956128C6 0xDF54AC89”.

The behavior doesn't change: the sensor LED stops blinking when I disconnect the serial interface and automatically starts again when I connect the serial port. When I disconnect the 5V, disconnect the serial port, and reconnect the 5V the sensor does not automatically start (LED steady red). 

I've also tried a factory default, but that also didn't help.

Am I doing something wrong? Can you send me the exact commands that I should use after a factory default?