*RESOLVED* Battery or Alternator?

Hello! I searched the best I could via phone for the answer I am seeking, but I am trying to make a time-sensitive decision on whether or not my issue is likely the battery or alternator, and depending on what it is, the vehicle goes to one place or another.

Up until today, my 2015 TRD Pro has operated flawlessly. It's well maintained, garaged, driven daily (more often than not), etc.

Today I fired it up as normal, drove to a destination, fired it back up after that as normal, drove to another destination, and when I attempted to fire it back up after that I am met with nothing more than clicks. There were no warning lights (battery or otherwise) while driving prior to this. I sat there for a minute and moved the key all the way before you turn it over and see the voltmeter I have in the cigarette lighter is reading about 8.8, sometimes creeping up just past 9. All lights on the dashboard illuminate, radio turns on, etc., but when I attempt to turn it over, I am met with clicks and a voltage drop.

I ultimately get someone to jumpstart me, so I take this opportunity to drive to AutoZone for a battery test. While en route to AutoZone, the voltmeter ranges up/down between 13.2 - 13.9 and the dashboard goes dark, comes back, goes dark, rinse/repeat. I do not experience any loss of power and vehicle seems to accel, idle at the lights, etc., with no issue while all of that was happening. AutoZone diagnostics tells me it's a diode in the alternator, but before I rule that as the culprit, I wanted to check here first.

AutoZone gives me a jump and I drive the 20-25 minutes home with the dash blinking completely off/on, radio cycling, etc., as if someone was turning just that functionality on/off, but again, no loss of power as it relates to acceleration, etc. Voltage continues to read about 13.2 - 13.6 or so on the way home. I park it, turn it off, and when I turn the key just before it would turn on, voltmeter once again reads 8.8 and of course does not start back up and only clicks. During that 20–25-minute drive home there were no warning lights (battery or otherwise) illuminating in the dash.

It's a 2015 TRD Pro with a battery from 2019. I greatly appreciate any insight!

 

Sounds very much like the alternator. If it was just the battery, I highly doubt your vehicle would act like that. Mine never has with a dying battery.

 

Did they test the battery? If it isnt’t bad and it can take still take a charge, then charge it before starting it back up again. Then see if there’s still a problem.

 

If it's from 2019 I would bet a new battery is due anyway given that some people report not getting more than 3 years out of a battery. Dying batteries can show all kinds of odd symptoms and can test fine if you just drive it. Even if your alternator is an issue, I can bet a new battery won't hurt.

 

Sounds like the voltage regulator in the alternator.

 

Thank

They did. While the vehicle was off, they were seeing ~10v, once they used their jumpack to get it started, they seen the volt range between 13.2 - 13.9 while running and their diagnosis machine pointed toward a diode issue in the alternator.

 

Hmmm! I recall him mentioning something along those lines as he stated he shouldn't see the range going back and forth so much from 13.2 - 13.9 if it were the battery. If so, does that still require a full alternator replacement? I called the dealership today and they quoted me shy of $700.

 

I know these are probably infamous last words, but if it is the alternator, the YouTube tutorial I watched does not make it seem like it's a $700 dealership job. I have no mechanic experience and have only done the barebone basics (oil changes, and other common things) over the course of vehicle ownership.

This is the video I watched.. 2009-2018 Toyota 4Runner 4.0 V6 Alternator Replacement - YouTube

Thoughts on someone with no experience?

 

I’m leaning toward battery, but I don’t think you mentioned mileage. If you’re over 150k, might be worn alternator brushes. About $20 if you’re capable of removing and installing the alternator yourself. You’d probably have to order online. Very easy fix.

 

I am at ~180,000 miles. I just went to double check mileage, and it STRUGGLED to even give a reading and took a minute for dash lights to come on. Voltage was around 6.6 and it just sounded funny. I did not try to turn it over of course. Maybe first step is to pull the battery, take to AutoZone and have them do a load test.

 

The alternator should be putting out ~14.4V. the alternator is probably shot, causing the battery to die.

Edit:. It looks like you figured it out.

 

You need brushes. It’s that simple IMO.

 

Where are you seeing an alternator for $20?!

Also, if I am going to replace that, are there any recommendations for aftermarket that are direct fit?

 

Brush holder assembly. Remove alternator, remove back cover from alternator, this is held in by two screws.

 

Alternator brushes.

 

If you can get at Autozone, NAPA, etc., do that. Brushes are essentially the same, and Toyota uses the same one for many vehicles. My dealership didn't have them, so I ordered online. I do these preventively now.

 

They all work like this, almost regardless of vehicle. This is a Gen3.

https://www.youtube.com/watch?v=71_kBhg6_-A

 

Tim is very thorough in his videos. Basics are remove alternator, remove back cover, remove old brush assembly, install new one, reassemble. When you get the old one in your hand, I'm pretty confident that at least one of the two brushes is almost gone.

 

Just saw that you may be uncomfortable doing this repair. If you have a friend who can do it, go that route. I just hate to see you drop $600+ for this.

 

Call around to different shops and ask what they charge to replace the alternator.

 

That's a really good video. I've done this to 4 of my old and sold trucks and to my old and sold FJ-40.
The first one I did was the '73 w/18RC, and it was difficult to get the alt. back on that bracket, until I noticed that the cast bracket had a sleeve pressed in on the cast bracket. I just used a small ball peen hammer to tap that sleeve to give it a bit of wiggle room and the alt. and bolt slid right in. I love DIY and helping my friends save money but, I do work for food and beverages.
And getting together with friends and having a good time is a must.

Edit. The sleeve is there to reduce the chance of the bracket bending or cracking when the bolt is retorqued.

 

So you get it. You could replace ten sets of brushes and still not be at the cost of one alternator. And my experience has been that 200k is the danger zone for those brushes.

 

So you've mentioned replacing those brushes. With their diagnostic machine pointing toward a diode, what are your thoughts on that? I might be getting my wires crossed here (not literally), but I am trying to learn and will gladly soak all of this knowledge up!

 

I'm just sharing my experience and looking at your mileage and symptoms. Here's something you can try: if you can get it running, and you see a low voltage reading while running, tap lightly to moderately (not hard) on the body of the alternator with a wrench or hammer while running. Please be careful of belts and fan and such. But if tapping changes the voltage, probably brushes. If not, still likely brushes - they may just be that far gone. I've never experienced a diode failure, but I believe those are replaceable, too.

 

Whata'ya know, turns out it was the battery. I took the old one to AutoZone for a load test and it failed. They also noticed the body of the battery had some swelling, and the posts had early stages of corrosion, but not terrible. I ended up purchasing a D35 Optima Yellow Top, hooked it up and drove to AutoZone for a full system test. The diagnostic machine gave a green light for the starting and charging system test.

Huge thanks to each of you who were willing to view and respond with ideas/thoughts/suggestions! I really do appreciate it.

 

Glad you got it! And maybe plan for replacing the brushes. They probably need it and are cheap. And they’ll strand you when they fail. Best to do those at your convenience.