I have the '04 S4 with Bose, infotainment, and XM radio. I'm thinking of selling off the Symphony II and the XM receiver for an aftermarket head unit with a motorized screen and nav.

Does anyone know if Onstar will still work with a different head unit? If so, how well?

Thanks.

I'm not 100% for sure with the Audi but with the other GM vehicles that sport the Onstar, when you replace the factory head unit, you just lose the voice prompts. The Onstar still works fine, but the voice prompts are programed into the factory radio.

Again, this is a "gestimate"!<ul><li><a href="http://www.crutchfield.com/i-rad1cdix/">Crutchfield.com</a></li></ul>

The STARMOD1 fully duplicates the interaction of the factory radio/OnStar system when installing an aftermarket headunit. It allows OnStarTM systems in General Motors vehicles to continue to operate properly after the factory radio has been replaced. The STARMOD1 provides automatic broadcast of incoming OnStar calls even when the car is turned off. This unit has a built-in amplifier that powers an external speaker (not included) and has a transformer that completely isolates any added electronics from the car's electrical system, ensuring safe and trouble-free operation