04 BMW 325i not charging/bad alt

[wirelessF]

Had to tow my aunts BMW 325i because it stalled out at an intersection. I tried:

Jumping it: Car dies out after, lights very dim
Battery swap: Car starts but my multimeter reads 11.4V when running

SO I'm guessing it is a bad alternator. However the battery light didn't come on to warn her.

What should I look at now? I want to see if it's a small fix (ie fusible link, etc) before I'll tell her to tow it to a mechanic.

 

[rshaw125]

Take the alternator off and have it tested.

 

[Trav]

Depending on the year this Bosch unit may have a simple to swap regulator and brush module.
Easy way to tell if that's the problem is to take a screwdriver and with the engine running touch the screwdriver on the metal cap on the back of the alternator, its right in the middle.
If its magnetic just swaping the regulator/brush module will take care of it, if not either the brushes are gone (easy to check by looking at them) or the unit has other issues like a bad diode trio (rare), commutator/slip ring, field coil, etc.

 

[HerrStig]

If I were going to throw parts at it, the regulator/brush assembly would be a good choice, however most electrical items are "no return". If it does not fix the problem you own it the parts anyway. Perhaps the shop manual could tell you how to test the brush/regulator assembly on the car. There is always the chance of failure of the wiring between the battery and the alternator.

 

[eljefino]

Originally Posted By: wirelessF

SO I'm guessing it is a bad alternator. However the battery light didn't come on to warn her.


This is an interesting clue, because back in the olden days this light was needed to excite the field coil. It gets +12v from a fuse and the ignition "run" position and grounds inside the alt.

I'm sure by 2004 BMW added all sorts of fancy stuff to obfuscate this. Does the light come on during the key on self test? Probably run by computers now.

11.4V is very low for a "good" battery running the basics of a car. I'd expect ~12.5V key off, 12.2 running. Wonder if there's something (like the alt!!!) with a heavy current pull/ short.

 

[Eddie]

I expect ~ 14.2-14.6 volts running ~ 1,500+ rpm. As stated, I'd remove the alternator and take it to AP and have it tested.

 

[wirelessF]

The battery light did come on during key on, so the bulb isn't burnt out.

I'll remove the alternator and get it tested. Overk1ll mentioned how easy to work on these things so I'll give it a try.

 

[OVERKILL]

Originally Posted By: wirelessF
The battery light did come on during key on, so the bulb isn't burnt out.

I'll remove the alternator and get it tested. Overk1ll mentioned how easy to work on these things so I'll give it a try.


If you want the page from TIS covering the procedure let me know

 

[wirelessF]

Originally Posted By: OVERK1LL
Originally Posted By: wirelessF
The battery light did come on during key on, so the bulb isn't burnt out.

I'll remove the alternator and get it tested. Overk1ll mentioned how easy to work on these things so I'll give it a try.


If you want the page from TIS covering the procedure let me know

Cool. I might need something to print out just in case.

 

[antonmnster]

This isn't a very easy alternator to take apart.

Used to be you could easily pop the brushes out without removing the unit from the car.

On this one the unit will have to come out and the air shroud come off. The brushes are right there. To get to the bearings, you need to unsolder the big three phase wires that come from the other half of the case.

 

[wirelessF]

It was a bad voltage regulator. Had a shop rebuild the alternator. All is good, except the rancid power steering fluid so changed that too.

 

[antonmnster]

I've been changing my p/s fluid every six months by extracting and refilling the reservoir one quart at a time.

After 2 years it's finally starting to stay red. Be sure to try to clean the screen at the bottom. That can get plugged, causing a "mooing" that people would probably think is a bad pump.

 

[wirelessF]

Originally Posted By: antonmnster
I've been changing my p/s fluid every six months by extracting and refilling the reservoir one quart at a time.

After 2 years it's finally starting to stay red. Be sure to try to clean the screen at the bottom. That can get plugged, causing a "mooing" that people would probably think is a bad pump.


Is it removable? I remember seeing a screw in the middle of the reservoir as I emptied it out. Also the factory crimped hoses didn't help either.

 

[OVERKILL]

Originally Posted By: wirelessF
It was a bad voltage regulator. Had a shop rebuild the alternator. All is good, except the rancid power steering fluid so changed that too.


Sounds like my wife's. I'm on like the 5th change of it (baster method) with RP ATF and I'm still not done. But the steering feels much better now, pump is quieter and the fluid at least looks like ATF and not diarrhea.

 

[OVERKILL]

Originally Posted By: wirelessF
It was a bad voltage regulator. Had a shop rebuild the alternator. All is good, except the rancid power steering fluid so changed that too.


Did you end up needing what I sent you?

 

[wirelessF]

Originally Posted By: OVERK1LL
Originally Posted By: wirelessF
It was a bad voltage regulator. Had a shop rebuild the alternator. All is good, except the rancid power steering fluid so changed that too.


Did you end up needing what I sent you?


Yep. This one had the alternator idler pulley and there was a dust cap covering the mounting bolt. I would've been confused trying to find the second bolt.

 

[wirelessF]

Originally Posted By: OVERK1LL
Originally Posted By: wirelessF
It was a bad voltage regulator. Had a shop rebuild the alternator. All is good, except the rancid power steering fluid so changed that too.


Sounds like my wife's. I'm on like the 5th change of it (baster method) with RP ATF and I'm still not done. But the steering feels much better now, pump is quieter and the fluid at least looks like ATF and not diarrhea.


Did the basting method too. With the location of the PS pump, I probably would not want to change that.

Also what do you use to lift up the front of the vehicle?

 

[OVERKILL]

Originally Posted By: wirelessF
Originally Posted By: OVERK1LL
Originally Posted By: wirelessF
It was a bad voltage regulator. Had a shop rebuild the alternator. All is good, except the rancid power steering fluid so changed that too.


Sounds like my wife's. I'm on like the 5th change of it (baster method) with RP ATF and I'm still not done. But the steering feels much better now, pump is quieter and the fluid at least looks like ATF and not diarrhea.


Did the basting method too. With the location of the PS pump, I probably would not want to change that.

Also what do you use to lift up the front of the vehicle?


For oil changes? I don't. I just drive the drivers side up on the curb.