While I was out today, my truck was fine until it wouldn't start. No clicks, no nothing.

Got out the jump box, engine started but immediately died. This happened about 4 times until I tried giving it gas on startup. It then ran fine other than an intermittent whine that was very similar to the noise you sometimes get after a stereo install. Tthis was happening even with the stereo off. No battery light on the dash at any point.

Went by AutoZone and they told me the battery is bad as far as cranking but they can't test the alternator if the battery is bad.

Drove home, where my voltmeter showed 12.6 at the battery with the engine off and a steady 13.7-13.8 with the engine running, but this is what was happening on my in-dash voltmeter. Driving, it occasionally went above 15V. My interpretation is the alternator must need replacement, but could a bad battery cause such fluctuations?



I have a 3-year-old Toyota battery with a 60-month warranty so in case it was just the battery, I went to Cherokee County Toyota and here's where I need a BS check. The guy reached down and pulled the plug off the side of the alternator and the engine immediately stopped. He said the alternator is almost certainly bad b/c otherwise the engine should keep running.

Can that possibly be true? Besides being counterintuitive, I had researched how to check the alternator at home and nothing I saw mentioned this method.

Thoughts, comments, experience, and theories all welcome.

If the battery tasted bad replace it and see what happens if the problem doesn’t change it will most likely be a bad alternator. A bad battery with a bad cell will show it is charging but will die when you go to start it, ? how old is the battery you have in the truck now? Pulling the plug off the battery is not a test check charging cold and hot engine alt will either charge or it won’t charge it is not rocket science.

That's the classic set of bad alternator symptoms.

It sounds like you misunderstood the mechanic. What he demonstrated was a dead battery, which got that way because the alt wasn't charging it anymore.

No way to tell if the battery is a goner as well until you try to fully charge it. BTW, if the battery is defective and you don't replace it, it will take out the new alternator as well.

Back in the old days starting the engine and disconnecting the battery was a way to check if the generator or alternator was charging...BUT it's not recommended with more modern vehicles because it can possibly cause damage to some of the electronic components.

That being said I'm surprised the "Tect" resorted to doing that "old school" test when he should have all the test equipment to do it correctly and not cause any further damage!!

But it does sound like the alternator is bad or going bad, i.e. the internal voltage regulator isn't functioning properly, your vehicle should of stayed running with the battery disconnected.

The thing I can't confirm is him disconnecting the alternator instead of the battery would be the same thing, I would think by disconnecting the alternator that would remove the alternator from the electrical circuit, not the battery, but I could be wrong.

Sounds like your voltage regulator is going bad. If it's at idle or driving the voltage should be at 13.5 - 14 volts. That's what the voltage regulator is for. 15 v and over is too much, that's overcharging. the regulator is in the alternator so it would have to be changed. I would still give the battery a good charge just to be safe.

Good luck.

BTW. pulling the plug off the alt. was an old trick on pre 90's cars, it does not work on newer cars.

Just clarifying, the service advisor pulled the electrical plug off the side of the alternator, he did not disconnect the battery. Don’t know if that’s 6 of one & a half-dozen of the other but just to be clear.

I like stated not sure if it does the same by disconnecting the alternator as it does to disconnect the battery for testing the alternator....but you had the battery tested and it's bad, I'm sure it's bad because the alternator has been overcharging it since you stated your volt meter showed 15+ volts...so even if you just replace the battery the alternator will also damage the new battery... so that being said I would replace them both.

Also just an FYI, disconnecting the battery DOES still work to test the alternator, at least up to about 2011 or so because I have done it on my own vehicles before I heard that it could possibly damage some electronics, then I stopped using that test.

bad alternator, will cause unstable amperage output also. i had it happen to me with my high output alternator, given the age of parts, i had everything rebuild.

If it's the original alternator in a 2007, I'd have no problem buying a new OEM alternator. I'm still on my original alternator in a 2005.

That’s my inclination as well. $313 online through Cobb County Toyota. Reman Denso is $202 at NAPA so essentially it’s a new OEM part for ~$110.

I'm having trouble finding the webpage for Cobb County Online parts, keep getting messages either saying "page not available" or "We're coming soon, we're putting the finishing touches on our online parts store...etc. etc."

Do you have a link??

I'd like to check out the alternator you are looking at, at all other Toyota online parts websites it seems all they sell are remanufactured alternators, is the one you're seeing a new or remanufactured(?), what's the part number.

Wow, good catch, I somehow didn’t realize Toyota sold remans in lieu of new parts. You saved me $110.


Cobb County Toyota

Thanks, I just wanted to know if it was new or not, if they are selling new alternators for 4th Gens I wanted to get one for mine to have on hand since I have never seen any new ones being sold even from Denso.

Edit: That same one you're looking at is only $215 from McGeorge Toyota.

2003-2009 Toyota 4Runner Alternator Assembly W R 27060-31021-84 | Toyota Parts

Hmmm…p/n are the same but MSRP is much higher on Cobb County’s site. Weird.

@AuSeeker - Even more weird...I was looking at the part again on Cobb County Toyota's parts site and the MSRP had updated to match McGeorge's. Bought it for $232, which is still less than McGeorge b/c theirs would cost $31 to ship. Plus it's available today.