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Old 11-29-2011, 08:10 PM   #1
zhenkaaaM3
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red battery light;help?

It just so happened that I was driving today and randomly my red battery light came on. It was not a steady red light, it went on and off. It depended on how many rpms the car was at. At a stop, the light would be off. Its on and off.

What would be the solution to my problem? I know this issue has been discussed but I never got a specific answer.

EDIT***
my OBC is playing games with me. I was at 12.3 volts with the car off, when I started it, it struggled for a milisecond to turn on but it started. The voltage went to 11.9-12.2 at idle. I tried this twice with the same symptoms. (low voltage when on, and slight struggle to start. No battery light was on at idle. While making this video, it seemed to go back to normal again. Something is going bad but dont know what it is. My voltage is not constant just like my battery light.
The belts are fine, everything seems to be in tact under the hood.

Last edited by zhenkaaaM3; 11-29-2011 at 10:55 PM.
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Old 11-29-2011, 08:15 PM   #2
jcns
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likely your alternator on its way out or battery.
get a voltmeter and check the battery volts (at the battery terminals). With the car running, you should see at least 14V, if not, you have a problem
Let the car sit a few hrs and check the voltage on the battery with the car off; you should see about 12V.
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Old 11-29-2011, 08:18 PM   #3
zhenkaaaM3
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Well if I'm not seeing 14v, what exactly is my problem? Alternator is bad?

Ill check voltage tomorrow morning. If its 12, then my alternator is fine? And if the battery is below 12, then my battery is bad?
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Old 11-29-2011, 08:51 PM   #4
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If it's below ~13.5V while running, most likely your alternator is bad. Battery should be above ~12 when the car is not running.
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Old 11-29-2011, 09:41 PM   #5
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I checked the car, it was 13.2v while on, and after driven for 30minutes. Going to 1 location, and then back. When I turned the car off, it dropped down to 12.4. The battery light was not on at all when I was already driving back.

How can I check if its definently my alternator? could it just be a bad voltage regulator?
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Old 11-29-2011, 10:02 PM   #6
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Ok, a good alternator will put out anywhere from 13 to 14 volts and can be measured (and best measured) at the output stud of the alternator (the big, heavy, red cable). If you get a reading lower than 13 volts, even at idle, there are several main things to look at; make sure the cable at the alternator is both clean and tight, make sure that the battery ground and battery positive are also clean and tight, check the belt to make sure that it isn't too loose or ready to come apart. If these things are all good, have your battery load tested, a load test will tell you if there 2 bad cells (cells that are partly or completely shorted out), therefore not holding 12 to 12.5 volts. If the load test is good, then its time to have the alternator tested, common cause of an alternator not working correctly is that the brushes and/or voltage regulator is bad (in most cases, the brushes are worn and not contacting the stator shaft completely if at all) . If its a Bosch alternator, you can get the voltage regulator/brush kit and "rebuild" the alternator in less than 30 minutes (a couple of screws), however, if the bearings of the alternator are worn or making noise, better to opt for a new or re-built unit (generally the bearings are good and it only needs new brushes).
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Old 11-29-2011, 10:05 PM   #7
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Not to jack this thread OP, But I have a similiar issue in my 00 323i, My issue is that my battery light (Red) comes on when ever I run my rear defroster, and as soon as I turn it off the battery light goes back off, I have never had it come on any other time then when ever I put my R defrost on.......Ideas?
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Old 11-29-2011, 10:13 PM   #8
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Need to check the same things, could well be that the alternator isn't putting out 13 or more volts and when you turn the rear defogger on, instead of the alternator suppling the current/voltage, the battery has to help. When the car is running, the alternators job is to power everything and still put voltage back into the battery so that the next time you go to start the car, the starter motor will crank and the computer will fire.
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Old 11-29-2011, 10:55 PM   #9
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bump
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Old 11-29-2011, 10:56 PM   #10
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dude, it's your alternator. My car did the same thing and I replaced it and wham bam thank you ma'am it was good to go.
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Old 11-29-2011, 10:59 PM   #11
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damnit I was really hoping it wasnt. I was hoping for a voltage regulator to do the job.
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Old 11-30-2011, 12:19 AM   #12
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Weird thing about alternators.. When they go out, the alternator part doesn't actually break. The rectifier is the usual part that burns out, not the windings. Replacement parts for the rectifier are dirt cheap. Its amazing they can cost soo much.
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Old 11-30-2011, 07:42 AM   #13
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Alternator. Output when car is running should be 13.7V to 14.2V. You can take it out and have it checked at Autozone.

Buy a rebuild Bosch at Autohausaz for $193 with free shipping. Comes with 2 year roadside assistance.
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Old 11-30-2011, 10:12 AM   #14
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Yea, thats true. But a bad voltage regulator could be causing the output not to reach 13.7 to 14.2v as well, no? I see people replacing voltage regulators and saving themselves $100. This might not be my case.
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Old 11-30-2011, 10:18 AM   #15
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Try removing and cleaning the VR, perhaps it will help. Usually the alternator will fail completely, ie. not provide any voltage/current. It could be on the verge of failure, though.
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Old 11-30-2011, 11:00 AM   #16
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Yes, it could be a bad VR. The VR is the electronics part of the alternator. I would spend a little more and just replace the whole alternator. I know from doing some work that you have to go in again and redo it because it breaks again or something else in it breaks. Don't buy aftermarket Precision China made radiators. They do not work and the replacements are even worse. You can spend over $200 for a VR and then replace the Alternator for $193 and not have to worry about the bearings going bad.

Take a look at this thread about VR and Alternator http://forum.e46fanatics.com/showthread.php?t=886274

If you have a 2001+ alternator, then your VR will only cost $59.


Please tell us what fixes your problem.
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Old 11-30-2011, 11:11 AM   #17
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hmmm my battery light is always on lol, it never goes away, its been on ever since i bought the car, I've put thousands on the car since i got it and i've had no issues. Can't be my alt or my battery, i think its a loose wire somewhere :/

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Old 12-09-2011, 01:34 PM   #18
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Apparently, the Bosch alternators come with either a round or rectangular plug. Any clue on how to determine which one? I know...just look but its not the easy. I have a bunch of S/C stuff there and it will be a minor PIA to remove just to see the plug.
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Old 12-17-2012, 02:03 PM   #19
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Quote:
Originally Posted by aeorozco View Post
Not to jack this thread OP, But I have a similiar issue in my 00 323i, My issue is that my battery light (Red) comes on when ever I run my rear defroster, and as soon as I turn it off the battery light goes back off, I have never had it come on any other time then when ever I put my R defrost on.......Ideas?
aeorozco did you resolve this problem? i have the same issue. whenever i turn on rear defrost, my battery light illuminates red.
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Old 12-17-2012, 03:30 PM   #20
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I dont understand all the folks that ask for advise and then never come back to tell us what solved the problem.

It is ashamed that it is not a two way street. Are people that selfish that they only want a solution for themselves, but dont want to contribute?

Last edited by BMWCaptain; 12-17-2012 at 03:30 PM.
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