took it to an alternator shop and tested bad like i figured. took that info to autozone and got a full refund. and the alternator shop sold me a brand new alternator for $210

Thanks for posting the process you are going through. Painful.

Good luck on the final solution. Let us know if all gets resolved.

Yet another data point to not trust the auto-parts alternator testers. I think the results are useless, and even believe that one time a parts-store bench test actually killed my alternator even more (i.e., was just worn brushes when I took it in, but the machine fried some more ... and I forget details but it may have also told me the alternator was fine :yikes:).

I now rely on on-car voltage measurements and then my own component level bench test. I expect the alternator shop's equipment is just fine, but we don't seem to have those shops any where near me.

Glad you finally got it fixed.

REGULATOR DIAGNOSTICS
 

Greetings,

New here, so I have a question perhaps someone can answer. I have 03 X5 and battery light came on, replaced battery a couple months ago, and now alternator died as there is no voltage coming out of it. This is water cooled monster. Changed one on my 545i a couple years ago, so I broke the old one open and the regulator readings across two terminals was open one way, and not the reverse continuity.

So my question is, I have found that most people say the regulator goes bad, so has anyone done any diagnostics on regulators, as in put meter on connectors to see what the reading is in ohms. I was thinking of rebuilding the old one I have had or just change regulator, but was wanting to know if anyone remembers continuity test.

Thanks

When "the regulator goes bad," I believe it is usually just that the brushes (part of the regulator) wear out. That is easy to see visually once you have it out.

Yours is a water-cooled alt, right? I remember seeing a thread on here not too long ago, where there was a bearing failure on one of those, at a fairly low mileage. You might want to consider that as something to preemptively repair.

Just so you know for the future, the "battery" light coming on is actually telling you the alternator is failing - the "battery" light does not indicate the state of the battery itself but the state of the charging system. :confused:

Given the full replacement cost of the water-cooled alternator, it is likely worth looking into repairing and/or replacing the internal components that have actually failed; as you suggest, the regulator is one possibility, as are the brushes, as mentioned by oldskewel.

REBUILDING WATER COOLED ALTERNATOR
 

Thanks, I am learning as I go, read everything I can on subject, and checked and bearings are not noisy, spins freely, so not knowing what is common problem, figured I would try to learn more before tearing it apart. Not an easy job to pull and change regulator only to find out it may be diodes bad, so will check these too while apart. I bought new regulator, checked continuity and compared to old one, and yes, I have continuity on connector of regulator on old one, but none going both ways on new one, so I suspect this is the problem, so was just trying to see if anyone else bothered checking regulator before wasting money. Sadly, most just keep replacing components without diagnosing, and dealers just want you to spend a grand for new alternator, and I am from old school, diagnose it down to component level first.

Thanks,

Do yourself a favor and avoid a returning headache by just purchasing a new alternator to replace your defective one. So suppose you do the regulator fix, 3 months later bearing whine comes into the picture. Then you will be back at replacing the alternator. By the way why did you not check the charging system when the battery light came on? It would have produced the results of a failing alternator.

NEW ALTERNATOR VERSES REPAIR
 

Thanks, and you may be correct, but I am old retired electronics technician, from the old school, from the repair over replace era. lol It was obvious when the battery light came on that it was alternator as I had replaced battery a few months earlier, doesn't take a rocket scientist to know the vehicle would not run for long on battery power alone. Was able to get home, barely, and battery was dead, wouldn't restart when I put on voltage meter. Charged battery, checked again, only 12.1 VDC while running. Checked connections at alternator, belt, etc., so pretty obvious.

So here was my reasoning, replacing costs up to $600. and a regulator is $60. and diodes are $6. each. So I pulled it apart and bearings are smooth and noise free, no sign of wear at all. Regulator has open circuit when doing continuity test, while new one does not, so I know there is a problem with regulator. Started to check diodes, one had corroded leg which was broken and one was shorted, probably what caused regulator to go bad, so with that, figured I was safe in just ordering the diodes and replace the regulator and in the end, I save several hundred dollars. Mechanics will just try to sell you a new alternator and with labor, hit you for a grand, some of us don't have the money to waste, bottom line, so will update results when I get diodes which I will replace all six given when one goes, they all will eventually.

Thanks,

Nice work, FREE-PPV!
Glad to hear you were able to isolate the actual failed components and replace them.