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I had a new, 130 amp alternator put on my 2005 Cobalt LS today with the 2.2L engine. Once it was installed the mechanic tested it and it's running high voltage, 15 amps loaded and unloaded. They're afraid that this could cause damage to the electrical system. I drove it to and from work and it runs fine. I had it tested by advance auto on the way home from work and they also tested high voltage (see attached image). Is this normal for a new alternator or is it faulty and should I habe gotten the 115 amp? I didn't know there was a difference and advance auto's web site said the 130 was an exact match for my car. Any and all advice would be helpful. Thanks.

 

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My cobalt also runs about 15v on a cold start, will drop down to 12.8-13.4 later on. I googled around and found this is normal for newer GM vehicles. My battery looks like the original part, unless it was replaced with an OEM battery (2007), and it isn't bubbling over with electrolyte so I'm not worried about it.

Try checking it on a cold start, then after the engine has reached full operating temp (~196 degrees). It depends on the voltage regulator sensing when the battery doesn't need to be charged anymore, so if your alternator always stays at 15v then it could mean your battery is going bad. Or could just be a bad voltage regulator.
 
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