[Xirgil]

But if you own the hardware there's nothing to legally prevent you from severing the power to whatever sensors/hardware onstar is using, no?

[CivBase]

Sure. As long as the software continues to work despite whatever you broke or disabled. It all depends on how forgiving the software is and how integrated the hardware is.

If manufacturers really want to collect this data, they currently have the power to stop you.

[sidewndr46]

the car may not even start, or may disable virtually all functionality until the problem is fixed if you do that