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Discussion Starter #1
Hi,


I've been member for awhile, and this is my first post. I have 2012 Pilot with about 96K miles. Recently, I've noticed a whining noise while driving, especially when starting to accelerate at complete stop. Yesterday while driving on freeway, only the battery light came on, so I exited the freeway to take side streets as precaution. At complete stop, engine seems as if it's shutting down, and whenever I tried to accelerate, the car seems hesitant to engage the gears. And when the car is able to drive, it won't go past 20mph. I can feel the car is trying to shift into higher gears if I press harder on the gas, but all I feel is the jerking and clunking from transmission. I was able to drive home slowly. This morning, I tested the battery with a voltmeter , and the voltage is less than 11V. I also couldn't start the car. So, this is indicative of a dead battery which was mostly caused by a dead alternator, I think. My question is, is this the alternator or transmission issue? Could a dead alternator not allowing transmission to change gears? Is there transmission computer controlling the gear shifting, and when there's insufficient voltage, the gears won't be able to change? Thanks for your help.
 

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Had to replace my alternator a few months ago about that same mileage. They start to whine before they go bad. Sounds like yours is on its way out.

Sent from my SM-N950U using Tapatalk
 

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This is definitely your alternator that needs to be replaced. The transmission is perfectly fine. Replace the alternator, charge the battery and you will be good to go.
 

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Discussion Starter #4
To update, it's indeed the dead alternator. I replaced the alternator, and everything seems normal now. What's weird is that the transmission would not change to higher gears from stand-still acceleration. I guess the transmission is voltage regulated somehow.
 

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The engine and transmission controllers likely conspire to keep RPM's up when system voltage droops. Just a guess, since there isn't a lot of documentation available on all the PCM code.

Meanwhile...
Alternator bearings are wear items, and the whine you hear is the bearings well on their way death. If you can catch the bearings when they first start to get noisy, they are rather simple to DIY replace. The front (drive or pulley end) bearing sees almost all of the load. If you are comfortable getting the pulley off and splitting the case, it's small work pulling the old front bearing and putting a new one on the shaft. I haven't needed to do any of this to my low-miles Pilot, but the other cars in the fleet have been victims of this treatment at my hands.

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The first noises that worn bearings make might be a squeak, progresses to a louder whine and on to a rumble. The vibration from the worn bearings is what causes the eventual mechanical failure in the rotor windings, so the earlier you can catch the noise the better the chance of saving the alternator before it fails.

Know also that a tired battery will kill an otherwise-good alternator. The extra effort spent on trying to keep a tired battery charged causes excess heat buildup, with winding and bearing damage closely following. The factory or any decent replacement battery has a service life between four and five years in most climates. Heat shortens that life, as folks in Phoenix will attest. There are easy tests you can do on the battery to help you anticipate failure. Those include a load test while watching terminal voltage, and a specific gravity test of the fluid in the battery cells. My annual maintenance protocol includes testing the gravity of the fluid using a tester you can buy for a few dollars at almost any parts store. Biggest part of the job is safely removing the caps over the cells. After that, the little eyedropper sucks up a sample from each cell, and the floating colored balls in the tube tell you the battery condition. If it's less than all balls floating, start shopping. If two don't float, start the buying and replacement process now before the car strands you.

This kind of easy PM can save you a bundle in total maintenance outlay needed.
 

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A whining alternator (versus a hum, grind or squeal from a bearing) if often from one or more shorted diodes in the rectifier/regulator.--there are 3 pairs to rectify a three-phase alternator. The winding current rises because of the short(s), and the windings and subsequently the case begin to sing. The shorted diodes cause a large increase in ripple current, which can get into the audio system as audible whine, and also cause lights to flicker, especially LED's. The shorted diodes cause the remaining diodes to work harder, where more of them eventually short (or open), and the alternator can no longer provide a DC voltage sufficient to charge the battery Then your dash light comes on.
 
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