'99 Toyota Avalon With Alternator Whine

Discussion in 'Import Vehicles' started by edge, Jul 15, 2017.

  1. edge

    edge Full Member

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    Please fill out the following to ask a question.

    MAKE: Toyota
    MODEL: Avalon
    YEAR: 1999
    MILES: 30500
    ENGINE: 1mzfe
    DESCRIBE ISSUE....
    The alternator whines the most during a cold start and gradually reduces in noise as the engine warm. Charging voltage is 14.0 volts at about 1500 rpm during fast idle and drop to only about 13.95 V voltage at warm idle. Usually whining can mean bad diodes or a bearing. What is the best way to diagnose ? I see some videos online that unplug the alt to test the diodes. Is this a valid test and will it damage the pcm/ecu ?
     
  2. billr

    billr wrench Staff Member

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    Measure AC voltage right at the alt output stud. If it is over 1V there is likely a bad diode. Alternators can whine for reasons other than bad bearings or diodes, some of which are non-critical.
     
  3. edge

    edge Full Member

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    30.5 VAC and 14.6 VDC at the post . So, it Looks like a bad diode. I guess the VAC indicates how much ripple?
     
  4. nickb2

    nickb2 Wrench. I help when I can

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  5. nickb2

    nickb2 Wrench. I help when I can

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    Many good DVM's will report back good readings, but these PDF's are good trusted source.
     
    Last edited: Jul 15, 2017
  6. nickb2

    nickb2 Wrench. I help when I can

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    In a 1990 toyota, I would not be worried about frying a ECU for removing neg post.

    But today's cars and trucks are quite different.
     
  7. nickb2

    nickb2 Wrench. I help when I can

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    Ok, me with a few beers and teriaky stir fry and a cat going stir fry also and a day off. I will stop posting before I post some Lemmy.
     

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