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Discussion Starter · #1 ·
2016 Acadia Denali
Alternator Charging Issues???

I don’t know if I have an alternator issue or not. I would like some input.
I should first tell you that I had a really old battery and I changed it in April of 2021. Seven months later, we went on a long road trip from Arizona to Texas. About 3.5 hours into the trip, the voltage meter was sitting at 13 volts. Normal is around 15. I checked the volt meter with a tester and it was correct. And I decided to head home because the car was not charging. The volt meter then went from 13 volts for approximately 28 minutes then it would charge to 15 volts for 4 minutes. This happened the entire way home. I changed the alternator with a brand-new GM alternator and it cured the problem.
My normal use of the car is within an hour of home for about 3 or 4 days a week.

This past Friday (April 1st, 2022), we left for a road trip to Alamogordo, NM from Arizona, which is about 5.5 hours away. We made it there with no issues whatsoever. However, the next morning we drove for 30 minutes to a place to wait for an event where we waited for an hour or so with the car off. Then we drove to our event. After 30 minutes more of driving, the volt meter showed 13 volts. After 2.5 hours of driving with the meter on 13 volts, we parked at the event. When we returned to the car, it started without incident and was fully charging at 15 volts.
It charged for about 15 minutes then went back down to 13 volts and started the cycle of 28 minutes at 13 volts then charging at 15 volts for 4 minutes.
I read in some thread that in these cars, the BCM can control the alternator to save gas. However, this was not an issue that we had during our first road trip with this car from Arizona to Utah in May 2020.

The charging was fine when the car was initially started, then after approximately 15 minutes the cycle would began again.
I am going to change the alternator AGAIN with a warranty new GM alternator. But I would like to know if this could be a normal condition.

Thanks for reading this long story and thanks for any input or help that anyone can provide.
 

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If you read the owners manual, you'll find that what you're seeing on the voltage gauge is normal. Have a beer and relax. Put your mind at ease - take the vehicle to a qualified shop and have the charging system fully tested. Readings with a volt meter don't show everything needed to know about charging system integrity. If you had done that in the first place, you may have found it unnecessary to change the alternator.
 
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Discussion Starter · #3 ·
If you read the owners manual, you'll find that what you're seeing on the voltage gauge is normal. Have a beer and relax. Put your mind at ease - take the vehicle to a qualified shop and have the charging system fully tested. Readings with a volt meter don't show everything needed to know about charging system integrity. If you had done that in the first place, you may have found it unnecessary to change the alternator.
Thanks .... I bought it used .. no manual I just read a GM document that said FUEL SAVINGS MODE BCM takes over ... Thanks for the comment
 

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Thanks .... I bought it used .. no manual I just read a GM document that said FUEL SAVINGS MODE BCM takes over ... Thanks for the comment
Owners manuals are available online. Here's the link to GMC's website where you can find one: MANUALS AND GUIDES.
 

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Yes mine has a RED line but it's at 8 volts What's up with that??
Agree the markings on many factory volt gauges are not accurate. One reason they went to digital numerals on newer vehicles.
You could also buy a plug in one of the many plug in volt meters that go into any of the auxiliary (cigarette lighter ) outlets.
I have one for my wife's daily driver and some also double as an extra USB power connect.
 

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Discussion Starter · #11 ·
Thanks ... The voltage markings are SPOT ON ... GM in their infinite wisdom ... put a variable alternator that cuts almost off (13.1 volts) when the battery is fully charged .... I found out that they did this because they got a Government subsidy to save CO emissions. After making the calculations it saved .245 mpg (yes less then 1/4)
 
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