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My wife was driving her 09 Cobalt LT with 90k miles on it, and out of nowhere her gauges started goin crazy (going back and forth rapidly), lights dimmed, stereo shut off, and then her car died. She had no idea if there was a battery light or check engine light because all the lights on the dash came on when it started acting up. Her friend disco'd the battery for about 5 mins and the car started and ran just fine and she proceeded to drive 45 miles home with no issues. I was at work when all this happened so I didn't get to see what it did. I checked all connections that I could think of (battery, alternator, ecm, fuse boxes, etc) and found nothing. I can't get the car to duplicate the issue. Anyone have any suggestions of what this could be? I thought it was the alternator at first but the car seems fine now. Oh and approx 6 mos ago she had the crankshaft timing sensor replaced, but other than that, just normal maintenance. Any ideas???
 

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Just some initial thoughts...

You might want to check your serpentine belt and make sure it's tight. Then start the car and make sure that the alternator pulley is rotating properly. If you have a multimeter (or can borrow one from an auto store), check your voltages. Battery voltage at rest should be between 12.4-12.7 V. When the car is running and the alternator is on, it should be 14-15.5 V. Anything dramatically less should tell you if there's something wrong there.
 

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Sweet. Thanks man. I buddy of mine has one so we'll give that a shot. The belt looks good and the alternator spins smooth n free when I took the belt tension off.
 

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Checking your voltages will hopefully at least eliminate a couple things. If you can, also poke around and check grounds all over the place. If things check out, we'll go from there. Tons of very knowledgeable people here! Check back for better answers lol.
 

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Battery is at 12.5 and the alternator is sittin right around 14.7. All the grounds I could think of seem solid and clean. Would the weather have anything to do with it? It was about 5 degrees out when it happened. But it's been colder than that and never had an issue. We're taking it to a friend that's an ASE cert GM mechanic tomorrow to see if he can find anything. My wife is driving my truck and we live on an Air Force base so I'm close to work anyways. But I'm gonna drive it to work n see if anything happens. It's acting just fine right now though.
 

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Well, that's some good news. I don't see how weather would cause those symptoms, however. And you said the battery terminals are clean, right?

If it happens again, I'd suspect a charging issue or short somewhere still. Is it possible that something was left on for a period of time before the car was driven? There may be/have been parasitic drag on the battery.
 

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I would check to see if boost post is loose. Even unscrew it and pull it tight again to scrape any corrosion.
 
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