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E46 M3 (2001-2006) Engine: S54 - Max Hp: 333 hp at 7,900 rpm / 262 lb/ft at 4,900 rpm
Total Produced: 45,000+ - Years Produced: 2001 to 2006.


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Old Fri, Jan-11-2019, 01:49:10 PM   #1
humarahumara
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Default Alternator going bad?

Need a little help from the experts....

Last night was doing a pull on the on-ramp when my battery light came on. It stayed lit all the way home (30 min drive).

Looking at past threads, 9 out of 10 times it's the alternator. This morning I checked the voltage at the battery and it was 11.91V. Low but still enough to get my car started. Figured battery wasn't getting recharged from the alternator.

Then with the engine running the voltage jumped to 13.8V. I assumed the alternator wasn't charging and it would continue to drop..but it's still charging.
Also battery light didn't come on.

Is this the first sign my alternator is on the way out? Something else like a bad battery? Any other tests I should perform? Should I keep on eye on it or just go ahead and get a new Valeo alternator? the alternator was not replaced during my 2.5 year ownership and miles are 110K.

Thanks!
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Old Fri, Jan-11-2019, 02:25:18 PM   #2
BigLooga
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Default Re: Alternator going bad?

Had the same issue, battery light would come on at roughly 4k rpm but would go away. I knew the battery was good as it was only a year old, check your battery first.

Replaced with a new Valeo alternator (easy to do by yourself except get the proper wrench for the fan clutch it was a ***** without) with a new one as i heard the rebuilt ones are a hit/miss.

Never had the issue after, car had 120k km on when it happened.

Good luck
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Old Fri, Jan-11-2019, 03:04:48 PM   #3
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Default Re: Alternator going bad?

Quote:
Originally Posted by BigLooga View Post
Had the same issue, battery light would come on at roughly 4k rpm but would go away. I knew the battery was good as it was only a year old, check your battery first.

Replaced with a new Valeo alternator (easy to do by yourself except get the proper wrench for the fan clutch it was a ***** without) with a new one as i heard the rebuilt ones are a hit/miss.

Never had the issue after, car had 120k km on when it happened.

Good luck
You could replace the voltage regulator portion of alternator, but, you would still have a unit with miles on it.....
Best bet is to replace the alternator - seen this scenario many times
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Old Fri, Jan-11-2019, 03:12:17 PM   #4
humarahumara
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Default Re: Alternator going bad?

Drove the car 30 min to work. Battery back at 12.6v with car off. I think the alternator hasn't completely failed but probably on its way out. I did change out the battery this past July so hopefully it's not the battery. Will check on the voltage of the battery later this afternoon and see where the voltage is.
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Old Fri, Jan-11-2019, 03:22:36 PM   #5
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Default Re: Alternator going bad?

If the bearings are good then you can just replace the regulator. The major wear items are the shaft bearings and regulator.


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Old Fri, Jan-11-2019, 03:25:21 PM   #6
Obioban
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Default Re: Alternator going bad?

Alternator.
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Old Fri, Jan-11-2019, 03:27:55 PM   #7
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Default Re: Alternator going bad?

Maybe double check that the nut hasn’t worked itself loose, but it’s almost definitely the alternator
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Old Fri, Jan-11-2019, 04:10:34 PM   #8
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Default Re: Alternator going bad?

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Originally Posted by terraphantm View Post
Maybe double check that the nut hasnít worked itself loose, but itís almost definitely the alternator
The nut for the positive cable at the back of the alternator? Will do. Battery clamps are tight.
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Old Fri, Jan-11-2019, 04:16:56 PM   #9
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Default Re: Alternator going bad?

If you replace the alt, insert the lower bolt with that alt out of the car and tap with a hammer (not bang...tap) to back out the nut on the back side. Otherwise it will be a total PIA lining it all up.


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Old Sat, Jan-12-2019, 05:38:32 AM   #10
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Default Re: Alternator going bad?

check the voltage at positive nut near the drug bin

Had the same problem and the nut was oxidized

disassembled it and fuly cleaned, NO PROBLEM since
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Discussing Alternator going bad? in the E46 M3 (2001-2006) Forum - Engine: S54 - Max Hp: 333 hp at 7,900 rpm / 262 lb/ft at 4,900 rpm
Total Produced: 45,000+ - Years Produced: 2001 to 2006. at BMW M3 Forum.com (E30 M3 | E36 M3 | E46 M3 | E92 M3 | F80/X)