I have a 2008 Chevy Avalanche and I just installed the AVIC X930BT using the Axxess gmos-lan-02 harness as well as the ASWC.  I also did the video bypass while I was wiring everything else.  After the install, no sound comes through the speakers unless I have the turn signal or hazards on.  If I have them on, the radio or CD plays just fine for as long as I have the blinker on.  So I know my speakers are wired correctly and able to produce sound, OEM sounds work correctly, Bluetooth works fine (although no sound without blinkers), and NAV works fine.  Steering wheel controls also work fine (took awhile to recognize the Pioneer, but I finally got it to work fine).

What is going on?  I tried bypassing using a relay and not just grounding the mute and parking brake wire, but that didn't seem to change anything going on with my problem.  I've also tested all my grounds multiple times and they are all good (I even took an extra wire to the car chassis).  Please help!  Thanks!!

You may find better help in an Avalanche forum, but on my last GM product (Saturn Sky 2008) I had to buy a special device to interface with the blinker system so that audio would pass through, I also lost OnStar until the device was installed. Even then it never worked quite right, the blinkers would sometimes click through the stereo and sometimes the stereo would not work at all until I used the blinker once to start the device. It was something like PAC OS-4 GM Factory Radio Interface... each GM product has a special variant depending on year and accessories (Onstar, Backup Cameras, GPS etc) so again, I would ask the Avalanche forum (or search there as I am sure this has already been addressed since it is a 2008).

Why GM had to "marry" their headunits with the body control computer (that handles lights, blinkers, chimes etc) is beyond me.

I'm not sure it's an Avalanche issue as it's more of the harness and head unit issue.  All sounds do work thru the head unit, just not all the time--it seems to be some kind of power issue to "allow" sound to be pushed to the speakers.  The Lan-02 is an all-inclusive harness made for my truck, however I think there is one wire that's not correct or the harness "computer box" is not working.  I've actually hooked up 2 different harnesses and they both worked the same (no sound without turn signal on). 

So...it's either me messing something up or 2 boxes are broken.  I'm guessing it's me and that's why I'm asking the forum.  Any experts installers seen this problem?

Actually, I just looked up my eBay purchases and that is what I used on my Sky, an AXXESS GMOS Lan-02 for GM Monsoon sound systems.