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Discussion Starter #1
Hello Everyone,

I've read through all the other topics in this forum about alternator and undervolt issues. So this is probably a quick answer for someone in the know.

My car is showing the battery / alternator warning light when I first start the car cold. The batter is an interstate 5 yr that was installed about 8 months ago. The car starts and begins with a voltage between 12.1v and 11.9v. The voltage loses a tenth of a volt every 2 or 3 minutes. After about 3 to 10 minutes depending on if it's cold or warm outside, my radio flashes on and off, then the voltage jumps up to 14.2volts and holds between 13.9 and 14.2 the rest of the trip. Also much less frequently, the voltage will jump up to 16, and I'll get a warning about lamp sensor and esp not available.

The voltage jump is telling me that the regulator is probably needing to be replaced, but I wanted to see if I should just go ahead and yank out the alternator also. It's the original alternator in an 03 with about 82000 miles. The undervolt and kicking in once it seems to get warm seems more mechanical and alternator related than something solid state like a regulator. Just want a more expert opinion before I buy both. At this point, I'm thinking that it might be a good idea to just replace both and the belt anyway.

Thanks, this forum has been an amazing help over the past few months. It's probably the only reason that I still have an 03 1.8l coupe that actually runs. :)
 

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2002 C32 AMG
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1,771 Posts
The regulator is bad. You can pull the alternator, but I doubt there's anything wrong with it.
 

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Discussion Starter #3
Thanks for the reply. I'll start with the Voltage Reg and see if that's all that I need.

Any recommendations on places to pick up the part, or is this something that's just easier to run down to the dealer and grab?
 

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'07 C280 4matic, '06 530i, '98 ML320
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If you are going to remove the alternator to replace the voltage regulator, you might as well have the alternator rebuilt - especially of there is an alternator rebuilder around where you live.
 

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2002 C32 AMG
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1,771 Posts
I would agree with pcy. Depending on the price rebuild of the alternator is a good idea. I believe the regulator can be replaced without removal of the alternator saving you the hassle. An alternator is actually a rather simple design. Replacement of the main bearing is a good idea though.
 

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Discussion Starter #6
Thanks. I'm just going to go ahead and get it all done while I'm in there.

Thanks for the help.
 
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