My understanding of OnStar is that you have to disconnect some things to -truly- disable it. (Probably to let people 're-subscribe' if they try to use the thing when they aren't current customers.)
Other systems... I can say my Maverick lets you select whether to have vehicle location data shared or not, but TBH I don't trust opt-outs. [0] I've also run into the issue on my said car, where my opt-outs got de-opted when the dealer runs updates.
[0] - Also as a side note, I've had at least one loan note in the past (from a larger bank) where they stated a tracking device may be placed in the vehicle. Not sure whether they sell that data.
Other systems... I can say my Maverick lets you select whether to have vehicle location data shared or not, but TBH I don't trust opt-outs. [0] I've also run into the issue on my said car, where my opt-outs got de-opted when the dealer runs updates.
[0] - Also as a side note, I've had at least one loan note in the past (from a larger bank) where they stated a tracking device may be placed in the vehicle. Not sure whether they sell that data.