Yes it's all CANbus protocol. Details listed above are from the 500Kbps "High Speed" GMLAN they switched to in like 2006. While typical OBD-II commands are still usable, the ones I'm focused on are arbitrary ID messages between powertrain nodes. ECM talking to BCM, TCM to ECM, and such. Proprietary packets not included under OBD.

Example; When you turn the ignition to On or Start now, the BCM verifies your key is correct over the "low speed" bus. If the key or key fob passes security, the BCM sends a request to the ECM over high speed bus to start the engine. This is how ONSTAR performs a remote start function without a key.

Knowing those specific GM commands could allow you to start your car using any USB/WiFI/Bluetooth CANbus device connected to the high speed network.. No longer is the starter connected to an ignition switch. And the old Class 2 data feeding the IC is a thing of the past. Everything is CANbus now, with multiple networks per vehicle.

What I verified above is some ECM and TCM packets constantly being broadcast on the HS LAN. There is plenty more interesting data in there depending on specific model. Mapping all this "unlisted" data provides a new meaning to "drive by wire."

BTW: It's actually legal to hack your cars ECU's now...