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 ?