I have a 2018 Chevy. I get emails from the dealership that tells me when a light goes off on my dashboard. OnStar will give me monthly reports about my driving tendencies (average speed, aggressive acceleration, etc.).
So now that I know big brother has access to my car, am I able to disconnect it from the grid?
With enough research into wiring harness diagrams and a little mechanical/electrical aptitude you should absolutely be able to bypass the onstar system controls, you could even probably isolate it to where it can’t send a signal to your control modules but it still sends a signal back to onstar so they wouldn’t be able to deactivate anything, but sometimes theories don’t always work out and when you see the wiring diagram there may be some curveballs the engineers threw in just to complicate things
Best approach is to put RF blocking tape painted with RF blocking paint over the GPS antenna. Then paint it again with car-color matching paint. You can also get GPS blocking devices that you can plug in to the car.
In extreme cases you can fashion a custom wooden antenna cover (carve it with chisels) and then line the inside of the cover with fine screen metal mesh (blocks EMF and RF) and aluminum foil (blocks RF). Then paint the outside facing surface with RF blocking paint, and then with color-matching car paint. Put tape around existing antenna, and then glue the wooden antenna cover to the tape.
Note that there appear to be laws on the books that make it illegal to disconnect car GPS systems, so suppressing or blocking the signal appears to be the "most legal" way to do it. But since the Deep State may try to kill us using remote control software takeover of the vehicle, I would say ignore the law since we are likely at war, and claim Law of War and UCMJ is in effect, and you are civilian taking measures to protect yourself from the occupying power and to NOT become a combatant or collateral damage (per your rights under Law of War).