In reply to:

---

Chevy cars have this in most of their stereos and it seems to work nicely, anyone know how they do it?

---

I had thought about SCV before, but I had not really thought about how they did it. It is on the stock chevy radios like you say, and since it just goes to the speakers from there, it has to be done in the stock head unit. My silverado doesnt have Onstar, so there was no special OBD wiring connected to my head unit. That means that the SCV has to have a signal in the factory wiring harness. Pretty handy to get to. On second thought, it could still be an OBD serial signal, but just in the same harness as the speakers and power. Need to do some research.