Cadillac here. I just unscrew the cellular antenna from the onstar module before leaving the lot. Looks like the onstar module is less conveniently located for bolts (it’s under my rear seats, I think it’s behind your screen), but that’s a good way to avoid collateral damage to other things on the same fuse. Since it’s a separate antenna from the gps, I even still get navigation, just without map updates. It’s all the good of a cell jammer, with none of the prison or fines. For now.