I've been doing a lot of searching since the last post. Canbus is still in the future for GM.

It seems that Chevy is still using something referred to loosely as the, OBD-II, Class 2, or J1850, network. The OBD-II terminal is a connector on that network. Many new Chevys have radios (particularly rds radios) that play a role on that network. Warning chimes play thru the FL speaker. Bose head units output a fixed level line output, and send volume commands to the amp. Steering wheel controls likewise talk over the net, I assume directly to the amp. Onstar uses it to control with the headunit (don't have onstar). XM radios can be controlled by the headunit, and cause the diasplay of text on it.

There are devices that will read and write to this network via a Serial connection. About $85.

An odd fact. The packets sent on the network are very small, just a few bytes of data. I guess this is so no one device can saturate the net.

I'll post some of the links I found later.