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///M3 Forum
The BMW E46 ///M3 is the M version E46 and puts out an amazing 333 HP and 262 lb-ft of torque at stock specs! There are an amazing amount of modifications for both the coupe and convertible models so read up and get started modifying your cars today!

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Old 12-07-2012, 06:29 AM   #1
Cayne23
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battery light

Today while i was driving my battery light came on. It stayed illuminated while i was driving. When i stopped i popped the hood and looked at the alternator. The belt is good. Is my battery dying? there has been times when i try to lock or unlock my car and.i have to push the button a couple of times. And another question. Could a low battery cause my tps sensors to not communicate and set iff my eml light? Plz help
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Old 12-07-2012, 07:26 AM   #2
Cayne23
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Maybe i should say also, that i was in second gear. I pushed my sport button to pass some traffic and thats when the battery light came on
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Old 12-07-2012, 08:02 AM   #3
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keep an eye out. Once the battery light started illuminating, in about a few days I ended up getting stuck by the side of the freeway as the battery drained due to a failed alternator.

I rebuilt the alternator for like a hundred dollars and it failed on me within a week.
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Old 12-07-2012, 08:35 AM   #4
Cayne23
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Yea my indy shop said 690+tax for new altenator. Anyone wanna buy an m3 with a new clutch? i cant take this anymore and neither can my bank account
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Old 12-07-2012, 08:42 AM   #5
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Didn't you just get your car?
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Old 12-07-2012, 08:49 AM   #6
MachRc
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Just make sure if it is the alternator(have it tested at a shop, usually free of charge) make sure you get a new alternator instead of a rebuild. ANd try avoiding draing the good battery. Its bad enough the alternator is going out, no need to buy an extra battery.
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Old 12-07-2012, 09:15 AM   #7
Cayne23
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Yea +1 on not getting a rebuilt. It will b oem. Yea i've had the car for 4 months and i've had to put in a new clutch, i need my tps sensors replaced and now the altenator. So like 3k i've had to spend on it in the past month the tps sensors r gonna get done when my alt gets replaced. This is my dream car but god damn it, its becoming a nightmare
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Old 12-07-2012, 10:44 AM   #8
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Can someone point me in the right direction for a diy replacing my alt thanx
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Old 12-07-2012, 11:08 AM   #9
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Quote:
Originally Posted by Cayne23 View Post
Can someone point me in the right direction for a diy replacing my alt thanx
This is why you have spent $3k on the car. TEST before you replace. It could easily be your battery. Randomly throwing parts at a car is always expensive. ESPECIALLY an M3.
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Old 12-07-2012, 12:01 PM   #10
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Will b close to 3k after alt install. How do i test? Me and my car r about 35 miles from home. My voltmeter is at home.
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Old 12-07-2012, 02:51 PM   #11
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Ok omw home from work. Car is completly warmed up, and the batt light has been off the whole time. All electronics inside my car are off, except for my heat. Its cold. 30 miles to go. Wish me luck lol
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Old 12-07-2012, 04:21 PM   #12
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you can do the non smart way test it like I did(not recommended but I didnt really care) start car, pull the positive cable and see if the car stays on.

On new cars doing this will turn off the car as there are failsafes, but not in the e46.

take it to an alternator shop/ independent
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Old 12-07-2012, 04:25 PM   #13
Cayne23
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Alright Choxor u were right. Gonna go to autozone and get my alt tested. Made it home. Popped off the batt cover and saw the batt had a good charge to it, indicated by the green dot in the sight glass. Tested the batt. 12.5 v when car is off. 14.8-14.9 with car running hmmm...... Yea, gonna get them tested tomorrow
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Old 12-07-2012, 05:42 PM   #14
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I just saw on youtube how to test the battery and alt using the test mode in the car. With the car off my volt reading was 12.5volts. Started the car and it went uo to 13.9-14.0. Turned on the heat, same thing. Radio on, stayed the same. Turned on headlights, 13.8-13.9volts. Turned on rear defrost and front defrost, 13.6-13.5volts. Turned on both seat heaters full blast, 13.5-13.4volts Reved the engine,13.7-13.8volts. Idled down, 13.5-13.6 with everything on. Is the alternator slowly starting to go?
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Old 12-10-2012, 04:39 PM   #15
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It sounds like your alternator. My car had the light come on while driving to work. I drove to lunch and it was off. I took it to a good Indy, and they said it was charging like crazy. They took it for a spin and got the light to come on. It turns out it was working only sporadically. Things like that never get better, only worse. It was a touch over $500 for the alternator, belt and one pulley. These cars use a lot of juice, so once it craps out for good it'll strand you.

I believe all of the alternators for our cars are rebuilt these days, even the shiny one from the dealer.
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Old 12-10-2012, 05:14 PM   #16
Cayne23
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Yea im tryin to baby it now. Going in the shop on thursday. Gonna get my tps sensors replaced and my alt. Here goes another 1000 bucks. Oh well, at least i'll b able to feel my cars full power again. Havent felt it in like a month. Being that it was tps failing, then release bearing broke, got a new clutch, release bearing, shift fork and slave cylinder. And then the battery light came on. Well on the bright side i have all these new parts in my ///m. Lol. Not bad considering i only paid 15k for the car and will have put almost 3k into it. Still below my 20k max limit for a car lol
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