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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 12-11-2012, 03:32 PM   #1
Fragger
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Unhappy Is it the Battery or the Alternator? PLEASE ADVISE!!

Hello my Bimmer friends,

Last night, I drove back from work, and everything was PERFECTLY normal. 2 hours later, I started the car and the Flashing Red Battery light kept going in and out. On my way back home, all lights came on in the dash, and eventually the car shut off to the side of the road. The AAA guy couldn't figure out how to tow my low, low car, so he jumped/juiced the car up with his portable jumper, that started the car right up and got my home... 1 mile away or so.

Reading here, everyone suggests that the Alternator is the culprit for the flashing red light. So I am all set and ready to order the Alternator, but I decided to do the Self Load Test on the car via the Internal Diagnostics.

Here's the readings I saw:

Key not turned ON:

Constant reading between 119 or 120

Key in ON position, BUT CAR NOT STARTED:

Reading starts at 112, but continues to drop consistently to all the way to 105, at which point, I shut the car off.


Other symptoms:

1. The car DOES NOT start, when I attempt it, quick clicking noises and lights going on and off, but the car wouldn't start...

2. The electronics of the car are still running, or Unlock/Lock with remote, internal LEDs and Trunk LEDs



With the information I have above, and without a Stress Test on the battery (because the car is immobile, I'd have to call AAA to move it), can you guys help me make an educated guess whether it's the battery on the alternator on the car?

I need some QUICK help on this guys, so your prompt responses are DEEPLY appreciated! Thank you SO MUCH for reading!
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Old 12-11-2012, 04:27 PM   #2
taylor192
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1. Remove battery.
2. Take battery to shop to have it tested.
3. If the battery is > 6yo then likely it needs to be replaced.

Why guess when you can test and get a definitive answer. Borrow a car or take a cab/bus if you need to, removing the battery is simple.
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Old 12-11-2012, 05:32 PM   #3
Fragger
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You're right Taylor...

Used AAA's battery service, sure enough, Alternator was fine, the battery was toast... got a new one for $148 plus 6 years of warranty!

Hopefully it was not the worst deal in the world? Thanks!
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Old 12-11-2012, 06:13 PM   #4
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NP, glad you got it tested.

You probably paid $50 too much, yet when you're stranded $50 isn't the end of the world. Dec 21 is the end of the world.
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Old 12-11-2012, 08:35 PM   #5
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Make sure to still test the alternator. A new battery will last a little while, but if it is the alternator, you will drain the new battery as well.

Run the same diagnostic test from the OBC functions. It should stay up near the 140 or 14.0 reading (volts) when running. If not, your alternator is not producing, get it checked or you will get stranded again.

Countless threads here and other forums will point you in the same direction.

Good luck
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Old 12-11-2012, 08:46 PM   #6
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Quote:
Originally Posted by MyNewRag View Post
Make sure to still test the alternator. A new battery will last a little while, but if it is the alternator, you will drain the new battery as well.

Run the same diagnostic test from the OBC functions. It should stay up near the 140 or 14.0 reading (volts) when running. If not, your alternator is not producing, get it checked or you will get stranded again.

Countless threads here and other forums will point you in the same direction.

Good luck
This!

I believe that it could still be the alternator.

Sent from my ADR6400L using Bimmer App
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Old 12-11-2012, 08:51 PM   #7
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Hi Guys,

Part of AAA's test was that it tests the whole charging system. The guys assured me and showed me the alternator test and it seemed like it was performing right where it should have been...! Wonder if that was enough...?
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Old 12-12-2012, 01:34 AM   #8
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Won't hurt to run the test yourself. I ran mine a few times after having mine replaced, just for piece of mind. Drove to work with the test running so I could keep an eye on it. Turn on the lights, radio, seat warmers, heater/AC...and anything else that will add to the load.

I actually had to have mine replaced twice. The first one would stop charging after the car got warm and the motor got over 5k rpm. Turned out to be a bad "new" unit. Indy replaced again and all has been great since.

Just monitor it for a bit, better to be safe and save your new battery.
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Old 12-12-2012, 10:05 AM   #9
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Originally Posted by MyNewRag View Post
Won't hurt to run the test yourself. I ran mine a few times after having mine replaced, just for piece of mind. Drove to work with the test running so I could keep an eye on it. Turn on the lights, radio, seat warmers, heater/AC...and anything else that will add to the load.

I actually had to have mine replaced twice. The first one would stop charging after the car got warm and the motor got over 5k rpm. Turned out to be a bad "new" unit. Indy replaced again and all has been great since.

Just monitor it for a bit, better to be safe and save your new battery.
Will do, bud... good call. So I am looking for readings in the 130s?
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Old 12-12-2012, 10:02 PM   #10
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UPDATE FROM TONIGHT:

Hi Guys,

Please let me update you guys on what's happened since last night, and then I would really appreciate it if you can chime in with what's going on! Please, I need some help/input!

So after the AAA guy installed the new battery last night, the lights went away. I asked him, do I need to drive it or anything to charge, he said, no, you're good.

I didn't use the car all day today, since last night. But around 12 hours later, I started the car WITH the built-in voltage diagnostics:

Without starting the car, I got readings of 124 - 125

I then started the car, and the readings remained at around 125 and the battery light was on again :'(!!!

I then gave it some gas... and BOOM, the readings jump to 14X and the light goes away !!

I stay idle just to make sure. Nothing changed, so I proceeded to drive.

I put the Nav on, bluetooth, lights were on, heat was at medium fan, and the readings throughout the drive remained between 139 and 140... no battery light!

5 or so miles into the drive, I pull into a parking lot and BOOM the battery light comes on, readings fall to 125 and keep dropping !!!!

I PANICKED and floored it towards my home! Did NOT want to be stranded AGAIN!!! I shut the heat off, turned the Dynavin off, no Auto lights, and take the phone charger out! The readings STOP dropping off at 119 and 120... Light on ...!

Now here's the twist.... for the 5 - 6 miles as I was flooring it home, the voltage NEVER fell below 119 and kept toggling between 119 and 120 ??? The battery light was SOLID this time for the MOST part, not nearly blinking like it was 2 nights ago...

I park in my driveway, and again the readings never fall below 119! I put load on, 118 AT MOST!

I then turn the car off, and leave it, come back 30 minutes later and the readings are:

124 - 125 WITHOUT STARTING the car
And with the start 119 - 120 fair consistently, with super load 118, at most, battery light on SOLID!


I am completely baffled on this now guys... Is it my battery that hasn't completely charged?

Why is my light now on Solid? (for the most part?)

Why isn't the voltage dropping while the car's started and did not for the 5 - 6 miles I drove it home?

Gassing the car is NOT raising the voltage this time... stuck at 120ish...


Can someone PLEASE guide me... is it my battery or the alternator?

Thanks for your help in advance, please do chime in, thanks!
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Old 12-12-2012, 10:08 PM   #11
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Sounds like the alternator, many times I have seen this happen, not just on e46s

People replace the battery, but that was already toast but holding enough charge to start you up and run for time while in the end both were bad, alternator and battery is something I've recommended to be changed at the same time. The alternator is probably oem in your car so it wouldn't hurt to change it.
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Old 12-12-2012, 10:31 PM   #12
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Quote:
Originally Posted by SATX_E46 View Post
Sounds like the alternator, many times I have seen this happen, not just on e46s

People replace the battery, but that was already toast but holding enough charge to start you up and run for time while in the end both were bad, alternator and battery is something I've recommended to be changed at the same time. The alternator is probably oem in your car so it wouldn't hurt to change it.
That's sad news, SATX... do you (or anyone here) know of a DEFINITIVE test for if it's the alternator or the battery failing? I need to know so I can order the appropriate parts...

Also, no chance in heck, that anyone here in Delaware would know how to install a new alternator, would they? I don't have tools, nor a garage/space to do it myself ...
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Old 12-13-2012, 01:09 AM   #13
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Alternator is still my diagnosis. It should maintain a reading at or near 140 or 14.0 volts when running. You should be able to put it under full load with little to no change...and by little I mean that it should not drop below 138 or 13.8 volts or so. This should not vary with engine speed.

The car will stay running until the battery drops down to about 11 volts or so, at that point you will not have enough to restart. Our cars do not run on the battery, they run off the alternator, the main reason for the battery is to start the car.
You might have a belt slipping, but again...this sounds typical to many many posts out here...

Search 'battery light' you will be amazed at the amount of posts with this in the title.

Again, don't toast your new battery, replace the alternator, then go out and enjoy your ride with confidence.
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Old 12-16-2012, 08:51 PM   #14
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Had simular issue, replaced battery and thought all was golden. Was recommeneded to take it to the local O'riley auto parts place as they have a tester they can put on the battery and check that and the alternator. Indicated that the alternator was heading south. Recently had replaced the power steering pump and added just a bit to much fluid in the resv and leaked some over the sides. Which happens to sit right above the alt. Easily replaced the alt (and belts whiel I was there) and alls good with the roof down.
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Old 12-19-2012, 09:19 PM   #15
Fragger
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Yeah... the alternator was replaced today. Seems to have done the trick!

Steady readings of 139 to 140 while started and running, via the on-board battery diagnostic test...

Thanks for the help guys!
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Old 12-20-2012, 12:13 PM   #16
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It's fairly simple. The voltage is produced by the Alternator. If the car is running and you see a battery light come on this is caused because the draw is GREATER than what is being produced by the alternator. Simple math, if the output is 320 volts and the alternator is supplying 300 volts then the remaining draw is supported from the battery.

When the alternator fails, you will draw power directly from the battery until is has depleted it's charge. With a normal battery is will inevitably take its toll and the battery will never hold a full charge. This is why dry cell batteries are better, even if after a full draw cycle it will still re charge to full power.

SO when you replaced the battery this is why the warning light was off and the car ran ok for a short time AND since the alternator was not producing enough output it again failed.

Good for future diagnostic tools!
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Old 12-20-2012, 02:37 PM   #17
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Yea its def the alternator. My light came on like 3weeks ago after pushing the motor to 6k rpms. I tested the battery with a voltmeter. Car not running-12.5volts. Car running,nothing on-13.9-14.0. Everything running, 13.6volts. I did the car self test, same results. I then talked to my indy shop. My mech said that actually if youre getting more than 13.8volts with everything on then there is a problem. Your system is over charging. In my case, my batt light hasnt come back on since. Could have been too high rpms. But its your alt dude. Its an easy fix. Autozone has one with a.lifetime qarranty for 145 bucks. Easy install. Therea diy's. But u dont really need them. The belt tension is automatic so just turn bolt move belt aside. Its easy
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Old 12-20-2012, 09:13 PM   #18
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I had the exact same issue as OP and it turned out to be a bad alternator. Good luck.
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Old 12-26-2012, 09:39 AM   #19
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Common thread it seems. Glad I'm reading this as we speak. My car had the exact same problem last night on Christmas, 3 hours from home. AAA towed to a place call Mr Alternator (Greenville, SC). they will rebuild the alternator this morning. parts and labor $250. Now I can make it home.
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Old 12-26-2012, 12:22 PM   #20
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Quote:
Originally Posted by Mr Dee View Post
Common thread it seems. Glad I'm reading this as we speak. My car had the exact same problem last night on Christmas, 3 hours from home. AAA towed to a place call Mr Alternator (Greenville, SC). they will rebuild the alternator this morning. parts and labor $250. Now I can make it home.
Assuming they do a good job, you found yourself a great price. Mine was a touch over $500 at an indy shop with a rebuilt unit. Even better luck considering that you really weren't in the position to do a whole lot of price shopping. Good luck on your ride home.
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