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DIY: Do It Yourself
Post here to share or improve your wrench turning skills! All BMW E46 DIY tips, tales, and projects discussed inside. Learn to work on your car and know the right BMW parts you will need!

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Old 10-01-2009, 12:06 PM   #1
nuwde
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Red Battery Light

Hey guys,

my battery light came on a couple days ago. i've been commuting with it and most of the time it's on, but sometimes it's off. the manual says it is not charging and the cause could be a malfunction of the alternator ribbed V-belt or the charging circuit of the alternator.

what are some steps i can take to diagnose the problem?

2001 car and has about 113k miles. alternator hasn't been serviced for the life of the vehicle, neither has the V-belt.

i also have UUC pulleys installed for over 30k miles but i don't think that has anything to do with it, plus never had a problem til now. please help!
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Old 10-01-2009, 12:09 PM   #2
brycez445
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I would put my money on the alternator. I had the same problem last year.
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Old 10-01-2009, 12:14 PM   #3
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the only time i ever saw my battery light come on, a few days later it totally died on me and i had to replace it. no problems ever since.
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Old 10-01-2009, 12:29 PM   #4
nuwde
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Quote:
Originally Posted by brycez445 View Post
I would put my money on the alternator. I had the same problem last year.
Did you replace the entire alternator, or did you try replacing the voltage regulator first? Is there an easy way to check the V-belt??
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Old 10-01-2009, 12:31 PM   #5
nuwde
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Originally Posted by brycez445 View Post
I would put my money on the alternator. I had the same problem last year.
Did you replace the entire alternator, or did you try replacing the voltage regulator first? Is there an easy way to check the V-belt??

Quote:
Originally Posted by Devious1 View Post
the only time i ever saw my battery light come on, a few days later it totally died on me and i had to replace it. no problems ever since.
What did you replace, the battery or alternator?
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Old 10-01-2009, 12:40 PM   #6
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Quote:
Originally Posted by nuwde View Post
What did you replace, the battery or alternator?
i replaced the battery.
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Old 10-05-2009, 09:42 AM   #7
naba2002
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i had this happen twice. once the car totaly died and only ran if i had jumper cables hooked up. so i got a new alt and a new battery and it was fine for a bit but still kept happening. turned out i replaced my alt with another bad alt. once a new one got put in its been fine for bout 6months now
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Old 10-06-2009, 12:54 PM   #8
nuwde
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the battery tested fine. finally got my valeo alternator out last night and will take it to a rebuild shop for ~$80 hopefully (over the phone quote). seems like it's the brushes so maybe voltage replacement will be even cheaper. will update later today. thanks!
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Old 10-07-2009, 01:03 AM   #9
nuwde
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got a rebuilt valeo alternator for $70 with 1 year warranty. battery light is not on and everything seems to be working fine now thanks for all the help everyone.
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Old 10-07-2009, 11:19 AM   #10
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If the battery light comes on while the engine is running, it indicates that the car is operating on the battery vs the alternator. Amazing how many people don't know this fact. It does not mean the battery is bad! It normally means that the voltage regulator is gone or the alternator itself. If your alternator was rebuilt for $70, the regulator was probably the issue. It's a $50 part.
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Old 10-07-2009, 11:32 AM   #11
nuwde
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If the battery light comes on while the engine is running, it indicates that the car is operating on the battery vs the alternator. Amazing how many people don't know this fact. It does not mean the battery is bad! It normally means that the voltage regulator is gone or the alternator itself. If your alternator was rebuilt for $70, the regulator was probably the issue. It's a $50 part.
Thanks hummer,

the alternator was completely replaced. everything for $70 also they probably wouldn't have given me a 1 year warranty on everything if he had just replaced the voltage regulator.

i took out the regulator and the brushes seemed like they needed repair. the core (part that makes contact with the brushes) also was not completely covered in copper. looked like a piece of it was missing.

drove my car home and started it up this morning. no problems!!
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Old 10-13-2009, 12:07 AM   #12
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$70 Alternator

Quote:
Originally Posted by nuwde View Post
Thanks hummer,

the alternator was completely replaced. everything for $70 also they probably wouldn't have given me a 1 year warranty on everything if he had just replaced the voltage regulator.

i took out the regulator and the brushes seemed like they needed repair. the core (part that makes contact with the brushes) also was not completely covered in copper. looked like a piece of it was missing.

drove my car home and started it up this morning. no problems!!
I just had the same darn problem with my 2001 330i (116k miles) where in the heck can i get that alternator deal you got please?
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Old 10-14-2009, 05:58 PM   #13
nuwde
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I just had the same darn problem with my 2001 330i (116k miles) where in the heck can i get that alternator deal you got please?
Sent you an email
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Old 10-14-2009, 06:01 PM   #14
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I could be the alt and the battery. I'll put my money on both
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Old 10-18-2009, 03:19 PM   #15
ComputerGeek
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I replaced the battery and the problem continued. I decided to just replace the alternator (Bosch 120) that included a new voltage regulator since my car has 116K. Used the DIYs here and now my BMW is back! E46Fanatics.com is the BOMB!!!!! Thanks to newde for the extra insight. BTW- I did not have to remove the fan. -

Last edited by ComputerGeek; 10-18-2009 at 03:23 PM. Reason: include the type of alternator
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