The aftermarket stereo is not canbus compatible. This is the communications bus used by GM for many engine and control functions. The steering wheel controls for example, work by sending a message on the canbus that the OEM headunit picks up and responds to accordingly. Well, the new headunit has no connection for the pink canbus wire.
If that had just meant that my steering wheel controls didn't work, that would have been fine. It went deeper than that. The van has retained accessory power. This means that the switched 12 volt line going to the radio is not just on or off with the state of the ignition. Oh no. Instead when you turn off the ignition, the body control module (I think thats the source) may instead leave the radio turned on even though the ignition is off. This means your music keeps playing even though your vehicle is off. Typically, the BCM will well and truely turn off the radio when the driver's door is opened. If you ask me, this is an overly complex system for not much payoff. How many people want to listen to music, turn off their car, and are not willing to turn the key back to the 'on' position?
The retained accessory power was not just controlling when to shutdown the radio, but also when to turn it on. When the car is started, the BCM supplies voltage to the radio. If the radio fails to send an "im on" canbus message within 10 minutes or so, the BCM powers off the radio. This renders the stereo useless.
So I had to install a Scosche GM3000. This installs between the factory wiring harness and the aftermarket radio. It DOES talk on canbus (aka GMLAN) on behalf of the radio. This means my radio now stays on as long as I want. The GM3000 also has a tiny speaker to play door chimes, warning chimes, and turn signal clicks. These were all played through the factory radio courtesy of canbus messages so they were all lost with just the straight aftermarket radio.
I then installed an Axxess ASWC-1 adapter. This thing also taps into the canbus to pickup steering wheel control messages. It then sends out variying voltages on a analog steering wheel control wire that the aftermarket headunit uses. Basically it takes in the digital signal and outputs in a standard analog format.
Initially everything was happy, the new headunit and both canbus adapters were all a happy family. Then, like any family, the fighting started. The Scosche gmlan adapter started playing the turn signal sound non stop and at a much faster rate, almost as if it was playing it several times on top of itself. This did not stop when the car was turned off. The only way to stop it was to pull the stereo fuse. This happened reliably after the car was run for maybe 20 minutes.
I thought that the Axxess adapter might be sending some weird shit back on the canbus line which confused the Scosche adapter. So I installed a simple diode on the pink canbus line going to the Axxess steering wheel controls. This prevented the Axxess unit from SENDING anything on canbus while still allowing it to READ canbus just fine. Now 4 weeks later and everything is still happy. The diode worked.
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