The alternator in my 2001 3.0i failed very suddenly like yours did, a few months ago at about 170k miles. After taking it apart carefully and fixing it, here's what I learned:

- The only problem was that the brushes had worn out. Surprising to me that this would cause it to abruptly go from working to not working, but that's what happened.

- Both Bosch and Valeo alternators are used in that era. The "alternator assemblies" of both brands are interchangeable - that includes the alternator, the voltage regulator (which is attached within the cover on the rear of the alternator, and is a separately available part, which includes the brushes), and the pulley (different diameters between the two brands).

- So if you want to replace the whole thing, including pulley, buy either brand.

- But if you don't want to replace the whole alternator, you can either replace just the brushes (soldering them in), or buy a new VR (which includes brushes). To be extra clear, the Bosch VR will NOT fit in the Valeo alternator, and vice versa.

- To do that, step one is to find out exactly what brand and amperage you have. Due to the existence of incorrect information, I would recommend looking at the actual alternator in your car. Don't rely on just looking it up. It can be seen by removing some of the intake items (takes a couple of minutes to do that), then with a flashlight, mirror, camera, etc. you should be able to find a label on the back of the alternator and take a photo for comparison.

- Once you have removed the alternator, replacing the VR is easy.

- My June 2001-build, model year 2001 3.0i E53 had a 120-Amp Valeo, so that would be my first guess for you, but as I said, I would look at the actual part in your car before relying on this or anything you can look up on RealOEM, etc.

I posted a summary of my repair on here somewhere.

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2001 X5 3.0i, 203k miles, AT, owned since 2014