Battery light came on for a few minutes, then back to normal.

J

Jonas

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Jul 13, 2020
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Hey fam! 2009 Pontiac Vibe GT, 238k miles. I stopped to get gas and noticed my car was idling high and the battery light was on. I got gas, car started back up fine, light still on. OBD said the battery voltage was 11.7-11.8 while driving. On my way home, the light just went off and my battery voltage stayed at 13.2-13.4v (normal for my car after driving for a while) for about another 15 minutes of driving - accessories on/off, driving/idle. Any ideas what may have caused the brief drop in voltage? My guess is my bluetooth OBD dongle because it does cause other lights and the gauges to twitch when not plugged in all the way, but I'm not sure. (Yes, I'm going to leave it unplugged unless I use it from now on ;-)
AAP tested my charging system and said my battery is good and alt is ok but on the low side, which again, is normal for my car after the battery is fully charged.
 
It may be something along the lines of an intermittent failure which will eventually become permanent. Our (sold last year) '03 Explorer exhibited similar symptoms for about a week before the alternator gave up for good. In your situation, I would personally remove the alternator and have it checked out by a local rebuilder, assuming you can find one with a good reputation.

Of course without some initial diagnostics/troubleshooting of the complete electrical system, we're really just guessing. I think it's a relatively good guess, though.
 
How old is the battery? Does the battery light go off it you give the gas pedal a little vroom vroom?
 
I think those have the same type of pulley that the Rav4 in this video does. The overrun type which will get weak over time and start slipping:

 
Same thing here. Its an early warning............Or something like that. LOL I would look into to replacing it sooner than later.
 
WobblyElvis said:
The brushes could be right on the edge of being worn out. They start to loose contact intermittently. 238K you got your money's worth.
Click to expand...
most alternators built in the modern era are brushless. work on induction, no brushes to wear out. but good guess if it was an old vehicle with a legacy alternator


all electricl charging and starting system troubleshooting should start at the battery... so the guy in question needs to load test the battery and determine if it is worth a s#i+ or not... then you test charging system at full electrical load at idle and see if it is keeping up... or remove alternator and have it bench tested... after that you need to look at the drive belt and tensioner if the problem keeps re occurring. if the problem isn't found by then its probably going to be weird.
 
MSCH said:
most alternators built in the modern era are brushless. work on induction, no brushes to wear out. but good guess if it was an old vehicle with a legacy alternator


all electricl charging and starting system troubleshooting should start at the battery... so the guy in question needs to load test the battery and determine if it is worth a s#i+ or not... then you test charging system at full electrical load at idle and see if it is keeping up... or remove alternator and have it bench tested... after that you need to look at the drive belt and tensioner if the problem keeps re occurring. if the problem isn't found by then its probably going to be weird.
Click to expand...

A 2009 Pontiac Vibe with a brushless alternator?
I don't have an alternator from a 2009 Pontiac sitting in front of me right now but......I don't think so.
 
WobblyElvis said:
A 2009 Pontiac Vibe with a brushless alternator?
I don't have an alternator from a 2009 Pontiac sitting in front of me right now but......I don't think so.
Click to expand...
try finding a rebuild kit for that... then you will see.
 
Here are some detailed battery voltage readings:
Just after cold start this morning: ~14.1 volts
Cruising once warmed up (no accessories) ~13.4 volts
Stopped in drive, all accessories on ~13.1 volts
Hot start battery test:
12.96 volts before start
9.18 volts during start
13.35 volts after start
The battery is a "die hard" lead acid from AAP just under one year old
The alternator has not been replaced in the 70k, <3 years I've owned the car. I don't know if it had been replaced prior.
 
MSCH said:
is the belt slipping?
Click to expand...
Maybe. I did install a water pump recently and have been hearing a little hissing with the AC on. I cleaned everything again and it seems to be quieter.
 
Leo99 said:
How old is the battery? Does the battery light go off it you give the gas pedal a little vroom vroom?
Click to expand...
The battery is just under a year old. Oddly enough, the voltage stayed pretty constant at various rpms when the battery light was on or off, fluctuating about 0.4 volts tops.
 
The numbers you have given do indicate a couple of problems, but no guaranteed answer.

The battery voltage should not drop below 10 volts while cranking. Weak battery? Faulty starter?

At one time, while driving, the system voltage was only 11.7 - 11.8. This is never right. Usually caused by a non functioning alternator.

The other numbers provided, such as 14.1 and 13.2 volts, don't tell us much as they are within the normal range of operation.

Make sure connections are clean and belt is tight. Should the situation get worse, the root cause will present itself.
 
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WobblyElvis said:
The battery voltage should not drop below 10 volts while cranking. Weak battery? Faulty starter?
Click to expand...

It depends when you measure it. During steady state cranking, it should not drop below around 10 volts. However, in the first fraction of a second of cranking, it is normal for voltage to dip as low as 7 or 8 volts, so if you connect a multimeter to the battery and set it to read the minimum recorded voltage, will may show a low value.
 
It just happened again. Voltage dropped to the mid-elevens (per 2 different OBD readers) while driving but the battery light didn't come on. I just cleaned and reconnected the battery terminals and alternator connections and everything was fine (a little higher voltage than before) for a while. Again, odd that it drops to 11.4-11.7 volts and stays there.
 
I also noticed both battery connectors ground out when tightening them, as in they only grab the terminals so much before they won't tighten anymore. I can rotate them both by hand, but I have to push really hard.
 
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