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2009 G8 GT alternator??

8K views 16 replies 6 participants last post by  Pete09GT 
#1 ·
Alternator stopped supplying a charge to the battery Sunday, Monday I changed the alternator and it seemed fine. The battery had died while driving but I got it home and we charged the battery and it showed good under a load test. The day after alternator replacement it stopped charging I guess.. could the new alternator have gone out already? Everytime we start the car it pops up a battery picture and says "service alternator" and under Engineering mode it shows less than 12V and battery charge is down under 40% from 78% the morning before. Need help its driving me crazy o_O
 
#2 ·
Bad alternators can kill a battery, and vice versa. Loosing charge over night is either a drain or a bad battery.
 
#3 ·
Not necessarily losing charge overnight, but my wife drove the car from home to work today with a short warm up period to defrost the window and it was at like 43%. Last night after she got home it was at 78%.

I figured since it pops up saying "service alternator" and then shows a battery light on the left side of the dash afterwards meant the car isn't getting flow from the alternator to the battery. Thought I'd get better opinions from you guys since we've owned the car for about a week

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#5 ·
When the car in Engineering mode reads the Voltage, it is around 11.8V to like 12.3V ish with the car running. The alternator I got was from Autozone, reman'd. It was the only place that could get me the alternator the next day since I needed to drive the car back to my home for work this week. The car had no problems right after I installed it, seemed fine for the roughly 110 miles I drove after alternator install. The next morning it popped up the light saying to service alternator

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#6 ·
When the car in Engineering mode reads the Voltage, it is around 11.8V to like 12.3V ish with the car running. The alternator I got was from Autozone, reman'd. It was the only place that could get me the alternator the next day since I needed to drive the car back to my home for work this week. The car had no problems right after I installed it, seemed fine for the roughly 110 miles I drove after alternator install. The next morning it popped up the light saying to service alternator
At ~12V, its reading the battery. The alternator is not putting out anything. With the engine off I would drain the battery a bit by turning on the head lights for a while then start the engine and monitor the voltage. It should be ~15V. If not, I'm afraid the Autozone alternator is not quite compatible with the G8 system. Hope others more expert with this issue can chime in.
 
#7 ·
The Autozone alternator fit perfectly, 140amp, it seems to be the same as everyone else's alternators. Could be wrong though. When we first put the alternator on it would read in Engineering Mode around 13.6 - 15V. I read the car has to "relearn" the battery after you disconnect it for a period of time and the "relearn" takes the car 8 hours to figure out. So after the new alternator was installed, the battery was fully charged but the car read it was at 0.0% and it was at 32.5% after driving for like 2 ish hours. Then overnight it "relearned" and said it was at 78%, but dropped after driving down to 42% this morning over a 1.5 mile drive to work with a short time running to defrost the window.

It appears that the battery is running out of charge while driving the car.

Can the alternator be tested at the post under the hood? Or only at the battery terminals?

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#8 ·
No question the Autozone alternator fits. Its the voltage control and feedback circuitry that may not be compatible. But you were getting 15V initially, that's good. That's why I suggested checking for 15V charging voltage again.

Yes, the re-learn for the battery monitoring takes quite a while. I drove for ~100 miles after replacing my battery and the % charge was still wacky. If you are checking voltage, the post under the hood is good. If you are checking alternator output amperage, you have to check right at the alternator connector.
 
#10 ·
I had my OEM alternator rebuilt with a new controller from a local alternator rebuilder. After I swapped it out, the battery light on the dash went out but the alternator was acting erratic. Dimming lights (prior to HIDs) outside and inside. I then bought a new one from Amazon, swapped it in, and there haven't been any problems since.

Go with a new ACDelco alternator and return that remanufactured AutoZone alternator. The time and effort it takes to replace the alternator isn't worth the trial and error of dealing with remanufactured and rebuilt parts.
 
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#11 ·
I've had good luck with Napa remans before.
 
#12 ·
Just ordered the new ACDelco alternator from Amazon. It should be here by Friday and then I'll try to dink around and put it on the car to see if that fixes that issue. In the meantime, do places such as Autozone do amperage testing at the alternator itself? This seems interesting since the alternator initially the day after purchase and installation would supply up to 15V, but after about one day just seems to have stopped altogether.

After the first alternator pooped out on me, we charged the battery overnight to full and load tested it which came back just fine so I would like to think the battery is okay. But I could be wrong and the battery could be junk =/

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#16 ·
Check to see if RockAuto has the alternator and use their 5% discount code. You'd be surprised. I've found some things cheaper, shipped, from them than from Amazon after the discount code.
 
#13 ·
Isn't there a fuse related to the alternator? Check that. Maybe fuse F11 above the battery.
 
#14 ·
Good call. I will go and check the fuses and such. Going to also look at the terminal connecting the battery to the alternator and make sure it is connected good. I am sure it was/is, but might not hurt to double check I guess

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#15 ·
Hmm, so I found the nut connecting the wire to the alternator to be a little loose. Tightened it and jumped the car and so far so good. Battery is charging and Voltage is staying 13.3 and above so far. Hasn't reached 15V that I have seen yet, but it's running and charging so that is good news! Still going to swap this alternator with the ACDelco one when it arrives and take this one back..

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