[RayLivingston]

Was driving my '07 335i running errands on Saturday, when it had the mother of all electronic freak-outs - EVERY idiot light came on, and the multi-function display was cycling through every fault known to man - ABS, BRAKE, DSC, BATTERY, ENGINE TEMP, OIL LEVEL, COOLANT LEVEL, TRANS FAIL, etc. The speedo was jumping all over he place, the A/C simply quit working. When the coolant over-hear light came on, I shut it down. Figuring this was some single, systemic fault, I plugged in the VPeak, opened OBDFusion, and saw battery voltage was all over the place, ranging from 11V to 18V. Ooops!

Long story short, did a roadside replacement of the alternator. The only replacement I could get my hands on quickly was a rebuilt, for, (YIKES!) $750. But, once installed (a ROYAL PITA on the road-side, BTW), all was fine. Went about my business, but the next day, with less than three hours driving time on the new alternator, it happened again, exactly the same way! I pulled the new alternator out, returned it for full credit, and have ordered a brand-new Bosch, which will be here in a few days.

My concern - I can see the first alternator dying - it was 14 years old, with 141K miles on it. But two in a row? Could there be something else going on? If so, what?? Battery tested fine, just a bit low on charge, but that was because the second time I disconnected the alternator and drove the car home on battery alone. And the battery is only two years old.

Is there anything else that could explain two identical failures so close together? I sure can't think of anything that could be wrong wit the car that could possibly kill the alternator. The car ran perfectly for those 2-3 hours, and there were NO faults logged, other than a long-standing (more than a year) EVAP test pump problem.

[lookalikehuuh]

Where did you buy that rebuilt alternator from locally? Quality of parts locally can vary wildly which is why when possible I try to buy from FCP Euro. I had a similar experience when I was forced to buy an alternator from Autozone when my original went out. Voltage fluctuated wildly on that Autozone unit. Replaced with a FCP unit and no more issues.

Did you happen to pull/clear codes from your car because im sure your car likely has tens of codes currently stored due to the voltage fluctuations.

[RayLivingston]

Originally Posted by lookalikehuuh

Where did you buy that rebuilt alternator from locally? Quality of parts locally can vary wildly which is why when possible I try to buy from FCP Euro. I had a similar experience when I was forced to buy an alternator from Autozone when my original went out. Voltage fluctuated wildly on that Autozone unit. Replaced with a FCP unit and no more issues.

Did you happen to pull/clear codes from your car because im sure your car likely has tens of codes currently stored due to the voltage fluctuations.

It came from the only local store that had one. It was rebuilt, I have no clue by who. It was either that, or have the car towed, then wait days for a replacement to show up. The new one, which will be here in a few days, is a brand-new Bosch, coming from oembimmerparts.com, which has been a VERY reliable parts supplier for me. On the first failure, there were a number of spurious faults flagged, which I cleared after installing the new alternator. On second failure, I shut it down much sooner, and now faults were flagged. I have not yet checked ALL controllers, just the most important ones - DME, TRANS, DSC, ABS. But, as I said, the car ran perfectly, with no faults on the above controllers, and no CEL. Immediately after installing the new alternator, and clearing code, the DSC light was still on but it went on its own out after driving a very short distance.

[mweisdorfer]

Originally Posted by RayLivingston

Was driving my '07 335i running errands on Saturday, when it had the mother of all electronic freak-outs - EVERY idiot light came on, and the multi-function display was cycling through every fault known to man - ABS, BRAKE, DSC, BATTERY, ENGINE TEMP, OIL LEVEL, COOLANT LEVEL, TRANS FAIL, etc. The speedo was jumping all over he place, the A/C simply quit working. When the coolant over-hear light came on, I shut it down. Figuring this was some single, systemic fault, I plugged in the VPeak, opened OBDFusion, and saw battery voltage was all over the place, ranging from 11V to 18V. Ooops!

Long story short, did a roadside replacement of the alternator. The only replacement I could get my hands on quickly was a rebuilt, for, (YIKES!) $750. But, once installed (a ROYAL PITA on the road-side, BTW), all was fine. Went about my business, but the next day, with less than three hours driving time on the new alternator, it happened again, exactly the same way! I pulled the new alternator out, returned it for full credit, and have ordered a brand-new Bosch, which will be here in a few days.

My concern - I can see the first alternator dying - it was 14 years old, with 141K miles on it. But two in a row? Could there be something else going on? If so, what?? Battery tested fine, just a bit low on charge, but that was because the second time I disconnected the alternator and drove the car home on battery alone. And the battery is only two years old.

Is there anything else that could explain two identical failures so close together? I sure can't think of anything that could be wrong wit the car that could possibly kill the alternator. The car ran perfectly for those 2-3 hours, and there were NO faults logged, other than a long-standing (more than a year) EVAP test pump problem.

$750.00 for an Alternator? Ouch

E90's usually don't like any alternator, unless it's a Bosch.

I would have it towed to the house and ordered the part from FCP Euro. You get a lifetime warranty & thats a good thing given how expensive an OEM alternator can be.

You might have been out a car for 3 days, but that's life. Better than the fiasco you've described 😉

Ah... lesson learned...

Did you consider changing out the voltage regulator first? It's a $35.00 part. That might have saved you $$$$

[RayLivingston]

Originally Posted by mweisdorfer

Did you consider changing out the voltage regulator first? It's a $35.00 part. That might have saved you $$$$

ZERO chance of finding one of those locally, or in a hurry, and, at 141K miles, this one has had a good life. The new replacement Bosch is "only" about ~$350, and has a good warranty. Besides, is that even possible? I took the cover off the old one, and the electronics all appears to be a single assembly, covering the entire back of the alternator, that is welded (literally welded, not soldered, or even silver-soldered) to the rest of the alternator. I was unable to remove anything.

[RayLivingston]

Ah! Now I see how the regulator can be replaced. The one screw holding it to the rest of the electronics was seized solid on mine. When I tried to loosen it, the plastic around it started cracking.

Any idea what the one small wire on the alternator is for? Idiot light? Battery voltage sensing? Excitation voltage? A sensing signal for the DME?

Output voltage IS entirely controlled by the alternator itself, right?

[RayLivingston]

The brand-new Bosch alternator I'm getting is more or less the same price as the cheaper of the two rebuilt ones from FCP Euro. Not sure what the difference is between the ~$350 one and the ~$650 one from FCP. One is "Bosch", one is "genuine BMW", but both are rebuilt, not new .

[e90yyc]

Difference? SFA.

Likely exactly the same model, but one has a sweet $300 BMW logo on the plastic cover where no one will ever see it. Apparently the magnetic field the BMW one creates adds at least two inches to your wiener, but if you’re like me and already have a hard time keeping your wiener from flopping down your pant leg and hitting the accelerator, I would probably recommend the Bosch.

Did you end up buying new-new, or rebuilt? Sorry—it wasn’t clear. If you went brand new, what did that run you?

[RayLivingston]

Brand new, Bosch. ~$538 including a $150 core charge. Free shipping. So, basically ~$400 net.

oembimmerparts.com

I've been buying from them for years, and they've been great. Good parts, good prices, and excellent service.

[e90yyc]

Seems like a good buy. Hopefully that solves your problem! Keep us posted.

[marvinstockman]

You need to get a multimeter, and use it to check alternator voltage. Use Youtube for a DIY.

[RayLivingston]

Originally Posted by marvinstockman

You need to get a multimeter, and use it to check alternator voltage. Use Youtube for a DIY.

I am quite familiar with how to check an alternator, and near 18V is NEVER acceptable. It was regulating properly for several hours, until it wasn't.

[mweisdorfer]

Originally Posted by RayLivingston

The brand-new Bosch alternator I'm getting is more or less the same price as the cheaper of the two rebuilt ones from FCP Euro. Not sure what the difference is between the ~$350 one and the ~$650 one from FCP. One is "Bosch", one is "genuine BMW", but both are rebuilt, not new .

You are paying an additional $300.00 for a BMW sticker 😂. Bosch is the OEM provider.

[marvinstockman]

OP, I'm so happy you know that you know, but the signal to charge comes from the car's computer, which is what you need to measure.

[Aj6543]

What about buying a cheap used one off ebay?

Also, I see there are two kinds of alternators? What's the difference between the one with a pulley wheel and the one without? Or are they the same?

https://www.ebay.com/itm/OEM-BMW-06-....c101196.m2219

[mweisdorfer]

You need Bosch AL0850X

https://www.fcpeuro.com/products/bmw...l0850x#fitment

[RayLivingston]

Originally Posted by marvinstockman

OP, I'm so happy you know that you know, but the signal to charge comes from the car's computer, which is what you need to measure.

What, exactly would I be looking for? I have no documentation on what that signal actually does, or what it SHOULD look like. Do you?

[Aj6543]

Also, can someone touch on the voltage regulator. How often does the voltage regulator fail? From my experience of owning three e90s, its always been the alternator that fails.

[RayLivingston]

If ANYONE here knows what the small wire on the alternator is for, and how it is used, please explain. It does appear there must be some means for the DME to exert SOME level of control of the alternator, but I can find no explanation of what or how. There are vague references to the DME tailoring charging profiles to the type and size of the battery, but is that signal an analog signal? A digital serial signal? An output from the alternator, and input to it, or both? What happens if that wire is simply disconnected?

[e90yyc]

Originally Posted by RayLivingston

What, exactly would I be looking for? I have no documentation on what that signal actually does, or what it SHOULD look like. Do you?

Yeah I’m also in for the answer on this.

Aj6543 How many alternator failures have you had? AFAIK there aren’t a ton of parts on these things that fail. I rebuilt my current alternator at around 200k miles, but that was mainly because it was a bit noisy.

What were your symptoms of failure? I guess I’m just thinking perhaps all you needed in one/some of these cases was a new VR??

[RayLivingston]

This gives some hints, but no details:

https://automotivetechinfo.com/wp-co...ng-Systems.pdf

This goes a little further, but still no details:

https://www.bimmerfest.com/threads/w...harge.1393181/

Only vaguely related, but if you ever need to know the battery voltage, and don't have a DVM handy, the car will tell you:

[RayLivingston]

It appears that small wire on the alternator is a LIN bus connection - a bi-directional serial digital "network" allowing the DME to communicate with the alternator. Here is a description of the LIN bus. BMWs are not the only cars to use this now.

http://www.testmyalternator.com/en/n...mmies-tma.html