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Thread: 97 528i - Alternator replaced, still not charging

  1. #1
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    97 528i - Alternator replaced, still not charging

    Hi everyone,

    My 97 528 started to show ABS, ASC, airbag lights during my commute. I stopped then couldn’t crank back up so had to get a jump start.

    First suspect was the alternator as the battery was 2 years old and the alternator started to whine for about a year.

    Here’s what I did so far :
    • Ordered a new regulator : didn’t help.
    • Got a scrap alternator : didn’t charge either
    • Got a brand new alternator : still no charge.

    The car drives fine with a charged battery (12.6V to 10.5V), it just doesn’t charge.
    I have the battery light on on ignition but it turns off with the engine running. Unless I unplug the 2 pin plug to the regulator in which case the battery light stays ON (normal behaviour AFAIK)

    • Tried a mix and match of 3 regulators on 3 of the alternators and still nothing.

    • I’ve checked fuse 15 which is fine.
    • Unplugged the oil sensor as I read it could mess up with the charging circuit, not better.
    • Checked all ground points which are clean and tight.


    • Tested the regulator connector, h
    ere are my readings (wire position is inverted from Bentleys manual, someone reported the same inversion on a BMW forum) :
    https://imgur.com/a/jTK61oq

    On my 2 wire plug, with ignition on :
    - First picture is bottom wire 12V = battery voltage (61E from Bentley's - green in my car)
    - Second picture is middle wire 8V (15 from Bentley - blue in my car)

    • I measured AC current at 0.04v which I compared to a friends well maintained and running car and he as 0.08v AC (Peugeot). So diodes look fine here.

    I do all my maintenance myself but I’m starting to loose hope and resign myself to bring it to a garage.


    I was hoping someone could point me to the right direction.


    Thanks in advance !

  2. #2
    JimLev's Avatar
    JimLev is offline Artifically Aspirated Moderator
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    Can you bring the alternator to an autoparts store that does free checks?
    Is F18 above glove box good?

  3. #3
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    Did you replace your battery? A failing alt puts a lot of load on a battery and can cause it to fail as well, even not charging.

  4. #4
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    Quote Originally Posted by JimLev View Post
    Can you bring the alternator to an autoparts store that does free checks?
    Is F18 above glove box good?
    Well I'm in France and there's no one here with a alternator bench test (not even big chains).

    I've just checked F18 with a multimeter, it's fine (0.1 Ohm), F15 is good as well.

    - - - Updated - - -

    Quote Originally Posted by TiagE39 View Post
    Did you replace your battery? A failing alt puts a lot of load on a battery and can cause it to fail as well, even not charging.
    Yes I did use a new battery after installing the second alternator. I do my tests with both batteries (2yo and new), fully charged and not.

  5. #5
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    Just a couple of random questions. What's the voltage at the Pos/Neg posts under the hood when the engine is running? It should be just north of 14v. Second, have you checked the underbody Pos cable connection? Could it be corroded and making poor contact?
    Current stable:
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  6. #6
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    Quote Originally Posted by padamdam View Post
    I have the battery light on on ignition but it turns off with the engine running. Unless I unplug the 2 pin plug to the regulator in which case the battery light stays ON (normal behaviour AFAIK)
    no, battery light should turn off when you unplug that.

    check your alternator's exciter circuit. I was also having odd charging problems like yours, then I backtracked the exciter wire and it turned out to be a blown diode inside the wiring harness
    Last edited by TiesTorN; 02-28-2022 at 01:53 PM.

  7. #7
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    Quote Originally Posted by E39 Newbie View Post
    Just a couple of random questions. What's the voltage at the Pos/Neg posts under the hood when the engine is running? It should be just north of 14v. Second, have you checked the underbody Pos cable connection? Could it be corroded and making poor contact?
    Well all my voltages at any point in the circuit is battery voltage (11.6 - 12.5). I never get more than battery voltage with the engine running.

    Yes I did check and clean all ground and positive points in the engine bay and battery compartment.

    - - - Updated - - -

    Quote Originally Posted by TiesTorN View Post
    no, battery light should turn off when you unplug that.

    check your alternator's exciter circuit. I was also having odd charging problems like yours, then I backtracked the exciter wire and it turned out to be a blown diode inside the wiring harness
    That's interesting, so connector unplugged, the battery light in the cluster should always be off (ignition and engine running) ?

    Do you happen to remember the location of the diode in the exciter circuit ?

  8. #8
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    it was in that wiring harness box on the engine;

    m62.JPG
    diode blown.jpg

  9. #9
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    Thanks, I'll look for it !

    What were your symptoms ?

  10. #10
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    Follow up,

    Turned out to be a stretched alternator belt.

    I had a whining/squeaking noise for about a year prior that I attributed at first to the power steering pump but it was the belt all along.

    Thanks for everyone you gave their input !

  11. #11
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    A whole YEAR???
    Set the controls for the heart of the sun

  12. #12
    JimLev's Avatar
    JimLev is offline Artifically Aspirated Moderator
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    Quote Originally Posted by BimmrMeUpSnotty View Post
    A whole YEAR???
    I was thinking the same thing.

  13. #13
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    It was a car in France so what did you expect? As a former tank driver he only learned to drive in reverse. Note: French tanks have three speed transmissions for reverse - Fast, Faster, and Full Surrender!

    Now that I have insulted France, I too wondered why some one would drive a year with a drive belt squealing and a low charge/no charge issue and not make the connection.
    Current Garage Highlights
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  14. #14
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    It’s ok, paybacks a b!tch, they insult us all day long… By the way, their tanks had one gear forward, fourteen in reverse.
    Set the controls for the heart of the sun

  15. #15
    JimLev's Avatar
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    ^_LOL, good one Stephen.

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    I consider cars like humans (yeah, I'm weird) and to me this sounds like year of torturing someone for no reason other than ignorance or laziness.
    Good all days of roadfly...
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