Car Stereos: Aftermarket audio in 2004 Chev Silverado, chev silverado, gm unit

Question
I want to install a Sony blutooth capable MP3/cd audio system in my 2004 2500HD Silverado. The installer tells me that he cannot do this without an expensive kit because the factory audio system (Not Bose; No Onstar) is part of the GM electronic diagnostic system and it would be compromised without the kit. Why can't the Sony be installed separately underdash, powered independently but using the already installed speaker and antenna wiring? Thanks.

Answer
Hi Peter,

As far as I'm aware, the only hardware you're missing in your truck would be the GM Interface that is required to keep your door chime as well as other audible warnings the car has.  That device is ~$50-100 and I would strongly recommend getting it to install a system on your car.

Installing the unit separately under the dash is possible, but would be very difficult, and cost far more in labour than the $100 GM unit.

Justin