'99 Toyota Avalon With Alternator Whine

edge

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#1
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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 ?
 

billr

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#2
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.
 

edge

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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?