The Class 2 lurks in the background.
I have a message about that and can even shed some light. What people don't know.
Originally Posted by cproaudio
All GM vehicles from 1999 and up are Class 2 databus compliant, however, it is not well known at all due to GM doing something for several years in vehicles like the S10, and Pontiac Grand Prix. Vehicles like this had an E&C/Class 2 hybrid bridge. Sort of like those old network hubs that had both B&C and Ethernet. Anyway, this bridge was used mostly for older electronics and Onstar operation, as well as many other functions such as the tamper resistant digital odometer, automated communications and timing systems (lights, remote keyless entry and passkey theft deterrent, chime, and even ABS and airbag systems) and other systems. Most people did not know that these vehicles had class 2 due to the fact that in most books, it stated that the serial data bus was usually the E&C or the ECMs Data I/O. If you get a pinout diagram of your BCM, you'll notice 3 different serial data buses. ECM data bus, E&C data bus, Class 2 data bus.
Of course, this got redundant and GM decided eventually that the E&C was no longer needed. Also, if you ever wanted to tap into the class 2 to add a newer device (such as a newer GM radio), you can. Most Class 2 serial data bus radios can be used in another vehicle as long as they are programmed with that vehicle's VIN due to auto theftlock.
Someone proved this fact with a 1999 Grand Am (usually known as an E&C vehicle). The link to the thread is below:
So don't be scared, it's there, and you may not even know it.