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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 Tue, Jul-06-2010, 03:57:10 AM   #11
RedM3/4
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If the battery still reads only 12v when the car is off, I'd seriously consider having the battery fully charged - get everything optimal. Older batteries do often have recovery problems after suffering a lack of charge, so replacing it was a good idea, but with everything you've posted I'm wondering if the new battery wasn't also significantly low when you put it in; it should be recoverable, but you're asking a lot of the alternator to do this.
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Old Tue, Jul-06-2010, 04:19:56 AM   #12
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There is no "reset" in the battery warning light - since it's an alternator warning light and is driven by the difference in voltage between the alternator and battery. As long as the alternator is making more volts then the battery - it's off.

As noted - 12V on the battery with the engine off - the battery is SICK. Miniumum standing voltage (after surface charge has bled off - like overnight) - is 12.6V. Less then that and the battery is at least partly discharged.
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Old Sat, Mar-14-2015, 06:24:10 PM   #13
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Default Re: Battery light AFTER replacing alternator and battery

speaking from experience...

If the battery light is still on after replacing both alternator and battery, then you should check the power cable from the alternator all the way back to the battery. I believe there are about 4 pieces in total. I bought 3 alternators lol and returned them after it didnt solve my problem. The problem was the cable that goes from alternator to the starter. I tested it and got no power. I decided to run a 4 gauge cable from the alternator to the jumper position and the light went away. good luck with it..


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Old Tue, Jun-30-2015, 06:28:21 PM   #14
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Default Re: Battery light AFTER replacing alternator and battery

I am having the same problem as the OP but in reverse. The battery light will occasionally come on during the initial start up and go off after around 3-5 minutes of driving. I have replaced the alternator with a rebuilt Bosch unit and Duralast Platinum battery AGM. I initially replaced the alternator and drove the car for a week without issue. The next weekend the battery died while I was driving and the battery light only came on right before it died. I then had to get towed even after trying to jump the car, the car would die once jumper cables were released while the car was running.

I am thinking that perhaps since the battery is now full it is rejecting any current sent from the alternator. Once the battery drains a small amount from driving it then is accepting of current which is when the light goes off.

Any help would be appreciated.
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Old Wed, Jul-01-2015, 04:54:35 AM   #15
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Default Re: Battery light AFTER replacing alternator and battery

Answer some of the same questions: what is the standing battery voltage, and did you have the cables cleaned well when replacing the battery and alternator? What is the charging voltage (running)?
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Most importantly, where did you get the rebuild alternator? The OP of this thread had a one-off problem compared to most. If you search, you'll find ENDLESS threads where the rebuilt alternator was bad. Some folks have gone through 3 or 4, especially if bought at one of the "big box" auto stores.

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Old Wed, Jul-01-2015, 02:45:23 PM   #16
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Default Re: Battery light AFTER replacing alternator and battery

It looks like the rebuilt Bosch unit is defective. The battery light is now consistently on and autozone is showing that it is only producing 11 V. FML.
I searched the forum and it looks like the quality control on the rebuilt Bosch units is less than stellar.
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Discussing Battery light AFTER replacing alternator and battery 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)