GMC Repair: Electrical or computer problem, gmc sierra, 2008 gmc sierra

Question
Tim
I have a 2008 GMC Sierra Denali. I love the truck when operating correctly, however it is parked outside with some time type of power failure. My recent experiences have been just driving down the road and parked went inside the store and came out and it was dead. No power, like there was a dead battery. I hooked up the battery cables and as I touched the cable to a negative or positive the horn started honking and the power was back up and running. This has happened three time in the past week. Currently it is parked dead in front of my house and this time the cable touching did not work. A friend told me he experience similar problems and just unhooked the battery cables which I plan to do and let it reset the computer and see if that works. In March this happenned I had it towed to the GMC dealer and they put a new battery in the truck and this made me look stupid. I need to take it to the dealer again. But can you please help diagnose why this is happening. I know with all the electronics that it is a chip somewhere gone haywire. Thank you for your help.
Charles

Answer
do you have XM radio?  if so has your three month trial expired?  If so the xm radio is stuck in a looping mode which will drain the battery, if this does not apply you have a draw somewhere in the system that needs to be isolated and corrected


by disconnecting the battery you turning off all of the modules, but when you reconnect the battery if you have a module, such as Onstar or XM that is being sent a signal and then gets stuck it will drain the battery.  If the vehicle is still under warranty, the dealer can perform some diagnostics to tell you if a module is looping.  We have had many with bad Onstar modules that kill the battery if just a few short hours