W-Body Car Audio

GM Class 2 Data Bus

In 2000, GM introduced what they dubbed the Class 2 Data Bus. The Class 2 Data bus allows the PCM (powertrain control module) to communicate with other parts of the car, such as OnStar. There's really nothing wrong with this until you want to install an aftermarket car audio system.

Basically, GM integrated the user interface of the Class 2 Data Bus into a familiar user interface: The radio. This sends chime signals to the front speakers, should there be something that needs your attention, such as the turn signal is on too long or OnStar tries to tell you something. If you remove the factory radio, you lose the chimes as well as OnStar. Removing the factory radio will light up the "Service Soon" dash light. The Class 2 Databus also checks for the presence of the amplifier, if so equipped.

If you want an aftermarket car stereo system in your Class 2 Data Bus-equipped GM, you have three options:

1. Keep the factory radio, using a line-level converter to supply an outboard amplifier with a signal
2. Keep the factory radio, using an amplifier with speaker-level inputs
3. Use a Metra 70-2003t adapter/headunit relocation kit with an aftermarket head unit and move the factory unit to the glovebox, console, trunk, etc.

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