FWIW I've investigated disabling the connected features on my 2019 Subaru Outback. The relevant module is the DCM, or Data Communication Module. It is physically located behind the infotainment system (what was once called the radio). There is a fuse that you can pull which will disable it (#9 I believe), but it will also disable the front speakers and microphone. This will break in-car navigation and Bluetooth phone calls.
Alternatively, if you're willing to disassemble the dash, you can remove the DCM entirely and replace it with a dumb plug that just reconnects the front speakers and mic directly to the infotainment system. One more caveat - some cars are missing a 5V power supply for the microphone, which is otherwise generated by the DCM. The signal exists on the head unit but is missing a pin, probably to save the $0.001 that this pin costs in quantity. You need to either add this pin, acquire that 5V supply from elsewhere, or install a voltage regulator that steps the 12V IGN supply down to power the microphone.
It seems that very slightly older Subarus have a problem with the 3G shutdown where the DCM goes into a braindead loop, trying to establish connectivity continuously and draining the battery. As a result, many shops are familiar with the procedure of finding and removing the DCM (to replace it with a newer one or reflash it, not sure which). Perhaps I'll see how much my local independent auto repair place would charge to remove it and replace it with the dummy plug.
Alternatively, if you're willing to disassemble the dash, you can remove the DCM entirely and replace it with a dumb plug that just reconnects the front speakers and mic directly to the infotainment system. One more caveat - some cars are missing a 5V power supply for the microphone, which is otherwise generated by the DCM. The signal exists on the head unit but is missing a pin, probably to save the $0.001 that this pin costs in quantity. You need to either add this pin, acquire that 5V supply from elsewhere, or install a voltage regulator that steps the 12V IGN supply down to power the microphone.
It seems that very slightly older Subarus have a problem with the 3G shutdown where the DCM goes into a braindead loop, trying to establish connectivity continuously and draining the battery. As a result, many shops are familiar with the procedure of finding and removing the DCM (to replace it with a newer one or reflash it, not sure which). Perhaps I'll see how much my local independent auto repair place would charge to remove it and replace it with the dummy plug.
See this thread for more information:
https://www.subaruoutback.org/threads/disconnected-cars-non-...