I know the iDatalink Maestro works with some European and US cars also. I don't know that there is any kind of standard. I suspect the unit has reversed enginee

I know the iDatalink Maestro works with some European and US cars also. I don't know that there is any kind of standard. I suspect the unit has reversed engineered the canbus messages for the different manufacturers. Before installing the unit you have to program it via usb. They provide software for Windows and Mac. You select your vehicle, wiring harness model and head unit model and it programs it appropriately. It also downloads pdfs with instructions for installation including wiring harness connections. For my Mazda no splicing of any of the factory wiring was necessary. For the Subaru I had to splice a single wire for the Starlink (similar to Onstar and not SpaceX Starlink related) unit. 3rd party headhunts from various manufacturers have a port for the iDatalink unit which allows it to integrate with the head unit. Both of mine are Kenwood but I know a few others have support. There are also alternatives to the iDatalink Maestro it is just what I have used.