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Bad alternator?

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Old Apr 22, 2010 | 02:58 PM
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rondocap
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Mercedes S55 AMG
Bad alternator?
So my my car would not start today. Battery was dead, had to jump it. It ran after the jump, and I took it to a mechanic - he put in a new battery, and it started up fine, but he tested the alternator and said it was failing.

So even if the car starts now, the bad alternator will eventually drain the new battery too right? What are some symptoms of a bad alternator?
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Old Apr 22, 2010 | 03:50 PM
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Jud Chapin
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Originally Posted by rondocap
So my my car would not start today. Battery was dead, had to jump it. It ran after the jump, and I took it to a mechanic - he put in a new battery, and it started up fine, but he tested the alternator and said it was failing.

So even if the car starts now, the bad alternator will eventually drain the new battery too right? What are some symptoms of a bad alternator?
Yes, the alternator must be putting out sufficient voltage, 13.5 to 15 volts or so, to properly maintain the battery. Too much or not enough voltage output is a problem for the battery. You can easily test the alt. output with a voltmeter.
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Old Apr 22, 2010 | 03:53 PM
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I was getting the voltage in the 12's, on idle and high rpm.
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Old Apr 22, 2010 | 05:00 PM
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Originally Posted by rondocap
I was getting the voltage in the 12's, on idle and high rpm.
That is the problem. The voltage is not high enough to maintain the battery. The problem does not necessarily mean it's a result of a faulty alternator, though.
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Old Apr 22, 2010 | 05:03 PM
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What else could it potentially be? Got a quote of around $800 to replace the Alternator.
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Old Apr 22, 2010 | 05:40 PM
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It could be as simple as a loose wire or belt. It could also be the voltage regulator.
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Old Apr 22, 2010 | 11:07 PM
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Or corroded contacts.
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Old Apr 23, 2010 | 08:55 PM
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OK, so it was the alternator. Battery was good. I got a new alternator put in, and it's perfect now.

The only problem...the parktronic system is not working. It turns off, and when on is on the red and beeping. Does it have to be reset? can I do it myself or do they have to connect it to the scanner and do it?
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