One last note which warrants a separate message. You MAY be able to find another vehicle with a similar system to be able to sniff it instead of needing the exact same car. The G8 is an Australian import and is very similar to the GTO. I believe the Camaro is also on the same platform and the new Impala/Caprice is also. You MAY be able to find out if they use a similar system and use them to sniff the information you need. They may not be 100% but might be close enough to get you what you need. You may also be able to accomplish this by wiring in the BCM anyhow and sniffing the codes. You should be able to tell which codes to ignore and only pull the ones you need. Then you insert those into your Arduino and ditch the BCM when you get it working. I am guessing the BCM will be giving you fits otherwise and may not work consistently in your system. You may get lucky and hook it up and it works however and my suggestion of many hours be off.