Battery dummy light coming on then going off..............

2001 325i 132,238 miles automatic transmission

Was on the freeway this morning and the battery light came on for a second. Then it went off. Drove for awhile and it did it again. 15 miles later I got to my destination. At the end of the day, now I'm driving home on the freeway it comes on, but now won't go off until I get on the gas. So I got off the freeway. I'm in front of Autozone, and before in the stop and go traffic the light would come on when I let off the gas a go off after I drove for a second or immediately.

I'm hoping this isn't an alternator issue. Please advice. Should I drive all the way home 30 miles? Is it possible something else like an under charged battery, which is less than a year old. I just bought one in Dec. or Jan. this year with the post to prove it.

Any help would be appreciated. Please and thank you.

Cheers,
William

Charge up the battery, but if it continues (which I suspect it will) it is your alternator. Buy a refurbished Bosch with the matching plug style and you'll be good to go. Mine died before 80k miles. Very easy DIY replacement, but make sure your battery is fully charged before swapping out the alternator. If it's depleted too much you could kill the new alternator too.

There are some easy checks you can do. Measure voltage at the battery at idle, then have someone increase RPMs to about 3000 or so. You should see the voltage increase indicating the alternator is charging. If the battery light is illuminated with the RPMs up, you will not see the voltage increase and this tells you the alternator is kaput.

Thank you for the help. I ended up replacing the alternator. It was pretty easy once I had the special tools to get the fan off. I'll tell you now though that I have a very noisy idler pulley which wasn't making noise before. Question, is it loose, or are the bearings going out on the pulley? I suspect the later.

Here is the old alternator that I pulled. Any idea where I could take the core locally to get the reimbursement, or at least dispose of it properly.







Thank you again for your help.

Cheers,
William

Originally Posted by Gaza77

Any idea where I could take the core locally to get the reimbursement, or at least dispose of it properly.

Why not rebuild it for about $30 and then keep it on hand for the next time you'll need it?

- Cn90 explanation of why you want to rebuild your own Bosch M54 alternator (1)

Originally Posted by Gaza77

Thank you for the help. I ended up replacing the alternator. It was pretty easy once I had the special tools to get the fan off. I'll tell you now though that I have a very noisy idler pulley which wasn't making noise before. Question, is it loose, or are the bearings going out on the pulley? I suspect the later.

Here is the old alternator that I pulled. Any idea where I could take the core locally to get the reimbursement, or at least dispose of it properly.

You are right on the pulley, they go bad all the time so you'll want to replace that one to quiet it down.

As for the alternator, the place you bought it from should have offered a core refund when you bought it... have you checked with them?

Bluebee,

That is a great idea! I probably won't have the car in two years (the next time it would need replacing), but I would love to have this type of project under my belt to learn. I have the bentley manual in pdf. Does it have detailed instructions to rebuild the alternator, and if it does not, do you know where I can find them? Also, I have no idea what usually goes wrong with alternators so would I typically be replacing brushes, or just cleaning the motor and lubricating it? Again, well said Bluebee, well said.

Cheers,
William

jhurless,

I bought the alternator from www.oembimmerparts.com and they do offer a core, but I would need to spend a good amount of the core money to mail/ship it back to them. I just figured local would be the same and get more of my money back, but Bluebee had a good idea to just make a project of it.

I plan on upgrading my Bimmer this year to something a bit more current, but you never know. Another working alternator might come in handy. I see you live in LA. Let me know if their are any core drop off facilities.

Cheers,
William

Originally Posted by Gaza77

jhurless,

I bought the alternator from www.oembimmerparts.com and they do offer a core, but I would need to spend a good amount of the core money to mail/ship it back to them. I just figured local would be the same and get more of my money back, but Bluebee had a good idea to just make a project of it.

I plan on upgrading my Bimmer this year to something a bit more current, but you never know. Another working alternator might come in handy. I see you live in LA. Let me know if their are any core drop off facilities.

Cheers,
William

I wouldn't have thought to rebuild it... that's actually a very cool idea if you have the time and interest to do it. As far as the places I know of, you buy the part from them and give them the core to get a fair portion of your money back. Pretty much no one rebuilds them anymore (in a shop for profit, of course), which makes the idea of doing it yourself all that much more interesting. Please post a writeup if you decide to do it. It could end up being a cool, and educational, project.

Originally Posted by Gaza77

Does it have detailed instructions to rebuild the alternator, and if it does not, do you know where I can find them?

We rebuild the Bosch & Valeo alternators all the time on the E39 side of the house; it takes only bearings, brushes, and if desired, a voltage regulator and/or diode block.

AFAIK, your E46 uses the exact same alternator as my M54 E39 (shown below).


PRO:
The advantage of rebuilding is that you put the BESTS PARTS in - and it costs a LOT LESS than a rebuilt alternator.
CON:
The downside is that it takes more time than just buying a rebuilt alternator - but - in your case (or in the case of someone who stocks the parts ahead of time), that isn't an issue.

Here are the links:
- How to test your alternator off the car (1) & how to determine exactly what alternator you have (1) & why rebuilding an alternator is preferable to replacing (1) & cn90 DIYs for rebuilding the I6 air-cooled Bosch alternator (1) (2) or his VW Bosch alternator (1) & cdawg246's quest for materials for a Bosch water cooled alternator rebuild (1) & Aioros' 1999 Valeo Alternator rebuild DIY (1) and his quest for materials (1) & Cn90's explanation of where to get hard-to-get alternator rebuild parts (1) & how to tell from the part number if a replacement alternator is actually rebuilt "by" Bosch (1) & a DIY for replacing the brushes in an (Audi) Valeo alternator (1) & a Bosch alternator bearing replacement from a 1997 MB S600 (1) & from a Range Rover (1).

Originally Posted by cn90

Nothing wrong with NAPA alternator. Infact, I called a few rebuilders in the US to get the detail (these rebuilders rebuild the Alternator and ship them to Pepboys, NAPA etc. etc.).

A proper rebuilding process involved. The issues for each item are in italicized letter:

1. New front bearing
- Some places put in new bearing but in 99% of the time, you get Chinese bearing instead of brand name like Koyo, SKF, F.A.G.
- Some check it, if no play, then they simple re-grease it and re-use it: not recommended.

2. New rear bearing
- Some places put in new bearing but in 99% of the time, you get Chinese bearing instead of brand name like Koyo, SKF, F.A.G.
- Some check it, if no play, then they simple re-grease it and re-use it: not recommended.

3. New brushes
- This is a must because at 140-150K when the alternator fails, the brushes are worn down.
So virtually all rebuilders install new brushes.

4. New Voltage Regulator (a.k.a = "Rectifier")
- Here is the kicker: if checked OK, most simply re-use it but read on.... Although this is a solid-state device (no moving part), it is rated at let's say 2 million cycles of alternator revolutions, then the solid state device just fails any time after that.
- The reason most rebuilders re-use the Voltage Regulator is cost (a good Voltage Regulator costs some $50-60/each).
- This is also the reason why many people run to Autozone, get a rebuilt Bosch Alternator, only to find out 1 month later the Voltage Regulator failed! Some in this forum have gone through 3 Alternators in a 6-month span. What a waste of time and effort!!!

Here's a picture of one of the two bearings and the diode block from the DIYs above:

This is an extremely useful post! Thanks Bluebee!

I will be looking into rebuilding the alternator as a great DIY project. I will take photos and perhaps also video of the project seeing how I'm a producer. I finally feel like I have something to contribute to the community. Thank you for the encouragement and help.

Cheers,
William

[QUOTE=Gaza77;7338709]Thank you for the help. I ended up replacing the alternator. It was pretty easy once I had the special tools to get the fan off. I'll tell you now though that I have a very noisy idler pulley which wasn't making noise before. Question, is it loose, or are the bearings going out on the pulley? I suspect the later.

Are you sure it is the pulley making the noise? I wouldn't touch a Bosch rebuilt alternator after one wouldn't even turn right out the box and two others sounded awful for the next three years (on different BMWs) until they finally died. Bosch just doesn't do a good job on rebuilt alternators.