Comment by quasse

The Toyota community has been far down that road with the DCM module in the new gen cars and found that the car still managed to get updates out to Toyota even with 50 ohm terminating resistors in the antenna connectors: https://www.tacomaworld.com/threads/simpler-solution-for-dis... (see the posts by user "Disgruntled Scientist").

Unfortunately simply cutting power to the telematics module also disables the in-car microphone for handfree calling. Fully disabling telematics involves making a bypass harness that re-routes the microphone and speaker signals past the disabled DCM module.