Quote:
Originally Posted by Boog
Glad to hear your power draw is fixed.
But don't be surprised to see the charging voltage go up and down. It's normal believe it or not.
Our recently purchased 06 Yukon began showing low voltage while driving at highway speeds. Down and up. It always started just fine. Since my wife is on the highway every weekend I want to do my best to make sure she don't get stranded out there. My first instinct was to replace the alternator. But before I did I did a little search online into charging system problems and found by OE design this alternator fluctuates charging voltage " as needed " as another means of reducing power draw on the engine and increase mpg. This is verified by some GM bulletins.
I've been watching it close and it stays fully charged. Wife's happy. I'm happy.
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Thanks for the reply Boog. I also looked pretty deep into the charging system for what my little brain could absorb and found that GM does indeed have a "charging strategy" for the newer vehicles. It is used to increase MPG like you said and also to reduce emissions which I guess is kinda the same thing.
After learning of this, I surmised that the alternator is not an "on and off" part anymore like they used to be. The strategy that I had read showed that the charging was controlled by the ECM but dictated by the BCM. The BCM would pick the appropriate strategy based on what the demand is at the moment. For example; charging at 25% at 2000 + rpm with no accessories on OR charging at 75% at under 2000 rpm with headlights and seat heaters on.
Knowing this, I had the Wife start it in the morning, turn on the heated seats and defroster to see if the BCM would be able to trigger the ECM to tell the alternator to charge. It wouldn't.
I guessed that the alternator had to have some sort of receiver to be able to take the signal that was being given by the ECM and some way of varying the charge rate as well. Given that the charging system was compromised by bad ECM signals for so long, I had guessed that whatever it is that varies the charge rate in the alternator had just gone kaput. I think we have it figure out now although Im not completely clear as to why. Hoping that this thing is fixed for now.
Like you say Boog - Happy Wife, happy life!