Vpad89

I might have found a solution to this issue. Alternator going bad. I have a 2015 Sierra SLT 6.2L and I was experiencing at random times intermittent power loss when I would attempt to initially crank. Seemed like the batt was dead, I would then attempt a second crank and would start up just fine with a “theft deterrent fault” displaying on digital screen with a caution light. Radio would even reset. I’d then turn off and crank a third time and everything would be fine, no lights or faults on dash. I took vehicle to autozone so they can check the battery and alternator and of course their little pack said everything was fine but I still believed either or was the issue because I would also at random times experience hyper flash while using turn signals with all bulbs and lights illuminating fine. I suspected it to be an issue with the power supply system. So it eventually got to the point where I would get the theft deterrent fault more frequent on top of a “roll window” fault and my alarm system going off for no reason after unlocking car and opening door. Turn signals were hyper flashing just about at every use at this point so I knew whatever the problem is was about to hit its worst point. I then decided to check the battery voltage using a voltmeter with vehicle on and noticed that the voltage was only reading about 12v with a/c max and headlights and fogs on. To me 12v seemed a little low, my interpretation is that it should be +13.5v with vehicle on and alternator charging battery. Even tho autozone said battery and alternator was fine I decided to replace the alternator anyway because I replaced the battery a year earlier. After doing so, I checked voltage again. This time the battery was reading +14.5v with max a/c and headlights plus fogs on. No more hyper flash or issues yet. Been a few days since. Never received a battery light during this dilemma so I can see why no one has figured out a possible issue with alternator. Autozone was no help, lol.