Swapped out the alternator today, works like a champ now, no battery light!

Maybe you can help me troubleshoot my issue too. Two days ago the ABS and battery light came on. The battery light would flicker, go out, come on but the ABS stayed on. Used the multi meter and had 12v with engine running, 10v off. Bought a rebuilt denso 80A alternator and replaced the old one tonight. The ABS light is now off but the battery light is on constantly. Testing again with my meter, i get 10v. So i took it to advanced auto for a warranty check and their meter tests it at 12.42v engine off and 14.6v running. My read is the battery is below 80% charge. They tell me they wont replace the battery yet.

Battery is an Optima Red top bought in 4/2012

So did my alternator kill my battery? Will my alternator eventually charge up the battery again? Truck runs great.

DrCoffee, do you have an update?

I have the same problem, (have not changed alternator, multiple sources tell me it's ok)

Thanks in advance!

I found the problem with my rig. There are three wires that connect the alternator. The white wire in the harness that monitors the battery voltage and tells the alternator to maintain voltage had a small nick in the plastic wire coating from the factory. Over time it corroded through and broke. So my alternator was running at full power perpetually. It also dropped my mpg to 17 because of the drag on the motor.

Check the continuity and voltage of each of the alternator harness wires. Mine is probably a unique situation but you never know.

In the end, I replaced the alternator, fixed the wire and kept the battery.

Update for me as well.....

Two days after I posted here I started seeing the gauges start going crazy (as others reported in other threads too with the battery light and/or ABS light) So, The alternator has been replaced and the issue is resolved. Sort of.

Looks like I have a valve cover gasket leak left front side that eventually is falling onto the alternator. Which would explain if it shorted the windings.

But as you know, it takes removal of the intake manifold to replace the valve cover gaskets. And with 295,000 miles, (I bought it new in 1996 ) i'm just going to let it slide for now.

Ive run into this issue as well. ABS and Battery light would come on and off but everything was working fine so I thought nothing of it. Then my lows stopped working followed by the high beams. So I went to autozone to check my alternator and the battery was too low on juice to test the alt so through warranty I got a new battery. Alternator checked out at 13.8 according to the guy and my headlights still don't work. Ive checked all the fuses and nothing is burnt.

What else could I check?

Thanks

Hello DrCoffee
I am experiencing a similar issue as your broken white wire at the ALT. How did you fix the broken wire.? Mine seems to be broken at the connector.
Lungfish

I pulled the wires out of the loom, found the problem and soldered in a new segment of wire a few inches back from the cut to make sure I had clean copper wire. If yours is broken at the connector, you may want to get a replacement connector either at Toyota or a junk yard.

I might start another thread as this is off-topic, but any opinions on these: High Output Alternator Fits Toyota 4Runner Tacoma Tundra 3 4L V6 1999 04 170A | eBay

Hey Dr. Coffee-

Are you talking about the positive alternator wire that connects under the gray plastic cover at the alternator?

I intentionally disconnected this wire from the alternator when I performed the big three upgrade. I wanted to make sure the current from the alternator only had one 120A fused path to the battery. Everything seemed fine at the time, but now I think I'm seeing my alternator not giving a full enough charge to my starter battery. Could this be the problem?

No. I am talking about the thin wires that plug into the alternator. Not the main power cable.

Gotcha, thanks.

As it turns out I was taking an invalid measurement of my alternator's idle voltage. I just finished installing my auxiliary battery's wiring and the truck had been running for more than 5 minutes. The solenoid had clicked on. The 13.3V charging voltage I saw on the primary battery was while the alternator was charging both batteries, not just the primary. When charging just the primary my voltage reaches 13.9V during idle, which I find acceptable.

Sorry to revive an old thread!!

Looking for some advice please!

My battery light came on about 2 months ago and stayed on. About 2-3 weeks later, I started having starting/cranking issues. Finally, it would not start. Then I replaced the battery and it cranked right up.

About 1-2 weeks later, the battery light was still on, but the engine was cranking fine. During this time, when I was having all of the battery light issues, I had the ECT button on constantly (not knowing this was to only be used in certain instances). In the 3rd week after replacing the battery, I started having cranking issues again.

Sometimes it would start up right away when I turned the key and other times, I would turn the key and nothing would happen. After turning a few more times, it would finally crank. Then I turned the ECT button off, and the battery light started to flicker on and off while the vehicle was moving until finally one day, the battery light just went off completely. I thought it was because I turned OFF the ECT button. Well, it appears that was not the issue. I am now having cranking/starting issues again.

I recently did a 3” coil spacer lift and did not put a diff drop in right away, so I had some grease flung out of the passenger side CV boot. I noticed that some of that grease got on the connections to the starter, so I cleaned that off really well. Haven’t driven it long enough to see if that helped the cranking issues, but today while driving, the battery light came back on!! I tested the output of the battery, alternator, and the starter without load and under load (multiple times) and everything was within normal volt and amp output each time. I have checked fuses and connections but can’t find anything wrong.

The previous owner did note that he never used the factory alarm (red button style beside the steering wheel. You know...the one that goes off like an SOB every time you disconnect the battery) as it could cause battery drain. But I have never had a problem with drain. Just that damn light on.

Please help!!

Sounds like an alternator that is slowly going out. The new battery didn't have cranking issues at first because it was full charged when you bought it. If the battery light is consistently on, then you can see what kind of outputs your seeing while running. Autozone can do this for free if you don't have a multimeter. Personally, I'd replace the alternator and see if your problems persist. If there is a problem with your alternator, you're not doing your new battery any favors by driving around with the battery light on.

Yeah, I don't believe you. If your alt light is on with engine running you are not getting 'normal' readings. Full stop. Either you don't know what normal is or you're doing it wrong. Spell out exactly what you did and what readings you got from where. Meanwhile, read my post upthread.