Alternator or battery confusion

proudrcf

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I have taken my 2006 Chevy Cobalt to two different places for an alternator check. They said that they couldn't tell me for sure if it's my battery or alternator. They said that the battery was very low but also the alternator was running low also so it was in decisive. I don't have a meter so i'm sorry for the sub info but he said my alt war reading at like 10-11 and should be at 13 to 14. Just looking for some sort of educated guess. I'm hoping its my alt cause i'm taking it to GM on friday and should be covered by warranty.

I had to jump it off last week because I left it at home for a weekend on vacation, once I jumped it off I drove it all week without a problem. Then this weekend I left it at the house for 1 day and had to jump it off. Any suggestions as to what it is, battery or alternator? Thanks for the help
 

RedDead

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It sounds like your alternator......if your alternator goes out first it'll drain your battery along with it....and that's what it sounds like man
 

YelloEye

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Sounds like an alternater issue to me as well, should get ~14.4v when the car is running.
 

UncleDave

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What did you find.

My battery will always show 15 volts when it starts then tapper down to as low a 12.8. The last trip I made, the battery was showing 15.2 volts for most of a 60 mile trip. This is high enough to break down the electrolyte and wreck the battery.

The book I have says the Regulator is in the Battery, then it also says the the Regulation is done in the Electrical Control Unit. Can't be both ways.

It ain't Broke, However is ain't right. Changed the battery as a first step.

Would like the battery to charge 13.8 - 14.2 or so.

Dealership should be able to help me out. No?
 

UncleDave

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Did not mean to lie, but I have a Haynes book, add it says that the Regulator is built into the Alternator. Then in the Diagrams it shows that the regulation is in the Engine Control Module: two wires running between the ECM and the Alternator, these being to control the Field.

When first started the Alternator shows 14.8 volts.

I usually start driving quickly, believing that the sooner the engine heats up the better the MPG. Once I am out of the drive, I have been trying different rates to get up the the Rated Limit. If the Volts goes to 14.9 or 15.0 it has tended to stay there, and go as high a 15.3: The other day, I had to wait for the wife, and let it idle a little bit longer. This time the Voltage did drop, and look more like a charge should be; 14.5 - 13.4.

The whole Idea of the battery in the rear is strange to me. VW stopped putting the engine back there for a very Good reason.

I have seen mention to checking the State of Charge when the engine starts. Any idea if this is so, and if so, How is done?
 

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