2006 Toyota highlander v6 new alternator not charging.

Joined
Apr 9, 2019
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My 2006 Highlander v6 alternator went bad. It showed low voltage and was making quite a bit of noise. It finally went out while driving and I had a battery sign come on. So I replaced it with a reman unit, but the voltage was still around 12.6v… so i returned it and bought a new Denso alternator. Finally replaced it today and now the voltage is still around 12.6v!!! There is no way I could have received two bad units (highly unlikely). I tested it with both a digital voltmeter and a battery load tester.

The car battery was recharged and the car starts fine and i can run it with lights on but the battery still shows 12.6v!

Is there a fuse between the alternator and battery?

Thanks!
 
Joined
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How are you measuring the voltage - with the car running, or the battery after turning off the car? 12.6v is likely fully charged for the battery. The alternator would put out more voltage only when running.
 
Joined
Apr 12, 2012
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Michigan
My 2006 Highlander v6 alternator went bad. It showed low voltage and was making quite a bit of noise. It finally went out while driving and I had a battery sign come on. So I replaced it with a reman unit, but the voltage was still around 12.6v… so i returned it and bought a new Denso alternator. Finally replaced it today and now the voltage is still around 12.6v!!! There is no way I could have received two bad units (highly unlikely). I tested it with both a digital voltmeter and a battery load tester.

The car battery was recharged and the car starts fine and i can run it with lights on but the battery still shows 12.6v!

Is there a fuse between the alternator and battery?

Thanks!

If it's anything like my 2006 Scion tC it's normal! I also remember thinking something was wrong with mine but turns out it won't charge the battery unless it absolutely has to and then it's only like 13.2v or something around there. I bet if you leave it for a couple days, let the battery discharge a little (car's computer can do that on its own) and start it up, check the voltage I bet you'll see 12.9-13.2v until it charges up the battery again.
 
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12.6 is a fully charged state for lead acid.

I must say from memory, my 2003 RAV4 charging volts at the battery terminals with the engine running was also well of 13!
 
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Oct 8, 2005
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GA
Raise the idle and see if it's charging. If so, clean the throttle body, relearn idle, then recheck voltage. It's super common to have to relearn the idle and/or clean the throttle body when unhooking a battery on that era Toyota vehicle.
 

Rayman

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Apr 9, 2019
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My 2006 Highlander v6 alternator went bad. It showed low voltage and was making quite a bit of noise. It finally went out while driving and I had a battery sign come on. So I replaced it with a reman unit, but the voltage was still around 12.6v… so i returned it and bought a new Denso alternator. Finally replaced it today and now the voltage is still around 12.6v!!! There is no way I could have received two bad units (highly unlikely). I tested it with both a digital voltmeter and a battery load tester.

The car battery was recharged and the car starts fine and i can run it with lights on but the battery still shows 12.6v!

Is there a fuse between the alternator and battery?

Thanks!
Thanks everyone!

So the idle was low when I started it this morning and I let the car run for a few minutes and even turned on headlights, radio and fan. At first it was around 450rpm and my multimeter was showing 12.5v. And after a few minutes it just kicked in and now is at 13.6v. I checked the rpm at idle and it was around 700-750rpm. Turned off the car and restarted it and the alternator seems to be charging. Turned on every accessory and it held the voltage around 13.3v. I’m assuming the idle was low and the car had to do some relearn or reset? Idk. But anyways it works now.
 

Rayman

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Raise the idle and see if it's charging. If so, clean the throttle body, relearn idle, then recheck voltage. It's super common to have to relearn the idle and/or clean the throttle body when unhooking a battery on that era Toyota vehicle.
Seems like the idle was the issue. Thanks
 
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Apr 12, 2012
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Michigan
Thanks everyone!

So the idle was low when I started it this morning and I let the car run for a few minutes and even turned on headlights, radio and fan. At first it was around 450rpm and my multimeter was showing 12.5v. And after a few minutes it just kicked in and now is at 13.6v. I checked the rpm at idle and it was around 700-750rpm. Turned off the car and restarted it and the alternator seems to be charging. Turned on every accessory and it held the voltage around 13.3v. I’m assuming the idle was low and the car had to do some relearn or reset? Idk. But anyways it works now.
Interesting how it seems to have "learned".. I know as I was saying before, there are times I wondered if my alternator (factory/original) was bad, but then it would wake up and do its job, not just once it acted like that all the time! Talking at the time to other tC owners same behavior! Glad yours is acting normal now and the voltage is around what I've always seen for our era of vehicles. (y)
 

Rayman

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Apr 9, 2019
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California
Interesting how it seems to have "learned".. I know as I was saying before, there are times I wondered if my alternator (factory/original) was bad, but then it would wake up and do its job, not just once it acted like that all the time! Talking at the time to other tC owners same behavior! Glad yours is acting normal now and the voltage is around what I've always seen for our era of vehicles. (y)
Yea. Seems like the vehicle had to relearn its idle. And once it reached the optimal rpm, the alternator kicked in. Seems odd though, because the alternator should work to some limit even at the lower rpm.
 
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All Toyota's with electronic throttle's have the low idle issue after any repair that requires the battery be disconnected for an extended period.

There is no published procedure to relearn the idle: you did it almost the correct way. The only change is to keep all loads OFF. Start the engine, loads off, and walk away. Let the engine idle for 30-40 minutes (or long enough for the fans to cycle twice) and you should be good to go.

Glad to hear it worked out.
 
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Feb 20, 2007
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The cruising voltage of my f150 is 12.4 when warm and the lights are off. Run the lights, or step the AC up to high, and it sets to 13.5. hits 14 or more at every deceleration, or when it’s first started. If the battery is low, and it seems like once a month, it will charge at 14.4 for a couple of hours, then return to its normal strategy. It also seems to disable start/stop sometimes for voltage reasons, but I haven’t quite figured out the pattern yet.
 
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