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Discussion Starter · #1 ·
2005 Tundra DC Limited. Battery light came on recently. I have had no problems starting or running truck. Ran my own tests last night and then took to local AutoZone to have them load test it, etc. Battery and alternator output tested in normal limits. I checked fuses (or at least the ones I found) and nothing.

This completes all the tests in the Haynes Manual too.

Thoughts?

thanks.
 

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You will still see 12v using a meter from positive post to chassis, 1/10th the cable will show you that.

Set your meter to ohms and check for resistance between the negative battery post and the ground on the chassis.

Set on DC volts, engine running, check the voltage on the battery post and then move the positive lead of the meter to the positive on the back of the alt. If your alt is putting out say 13.5 volts but you still only see 11 or 12 at the battery post, the cable between the battery and alt is dropping voltage.

You also need to check the positive bus for the underhood fuse box, make sure its not dropping voltage either.
 

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Discussion Starter · #6 ·
I will do these things, but I think I may have inadvertantly identified the problem. Last night, I drove it at highway speed, and the voltage needle began to bounce up and down. Stopped at an auto parts store and tested it again with me revving up the truck to 2,000 RPM. ALT output was almost 17 volts. Time for new ALT/regulator, I would think?
 

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2019 Toyota Tundra Platinum Crewmax 4WD 5.7L
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Checking the cables for corrosion and loose connections is a whole lot cheaper than a new alternator. It still could be the alt, but as Remmy and others have suggested here and in many other similar posts, these loose connections will also cause these kind iof headaches. For example, I have a small John Deere tractor that wouldn't keep a charge on a battery. It took three battery replacements (two under warranty) for me to find a bad cable, not a bad battery or charging system - and the problem was resolved. That silly thing is that the cable was less than a foot long. So...the moral of the story is don't overlook the obvious like a bad connection or cable. It's been known to happen. And if it turns out the alternator was the culprit, then there's plenty of info on the Forum about those items as well - including thoughts about where to buy and where not to. Good luck!!
 

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All these answers are right on track; but one thing mentioned here "17 v" gasp my attention... Once you have check and corrected any bad connections/corrosions at any terminal. Disconnect the battery from the veh and perform a load test to the battery to find if is "STARTING TO GO BAD" then if you have the equipment perform a load test to the alternator while "ENGINE IS ON" while testing the alternator keep an eye on the voltage gage... 17v is way out of normal specs...12.6 is a new battery any other readings are fora used battery. about 13.5 to 14.5 is a "normal charging rate. 16v it is CRITICAL VOLTAGE to too many on board components.... which to me tells me that the regulator is falling... Good luck! And post
Your findings as soon you find the issue....
 

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NO, not a bad alternator!!!


Typical toyota... battery type terminal on + terminal with nut on top... corrosion builds up between the layers (bottom is heavy copper flat going to starter terminal.) Next few are always leads to relay box, alternator sense, etc. If the alternator sees low voltage to battery due to corrosion in between layers on this, it will think it is charging a low battery and crank up the voltage. 1. Clean battery terminals. 2. take the 12-14mm nut off the positive post and clean in between ALL the stacked leads on there. Wire brush and corrosion spray is your friend.
Put it all back together. Measure with a voltmeter between neg post on battery to engine block with engine running. Should read close to 0. If you have voltage there, clean and check all the grounds going to the engine... (remember the alternator is grounded to the engine) a 3 volt loss in ground will show 17 volts charge. (alternator will think it is charging a battery to 14V)
Just remember the voltage at the post of the battery isn't always what the alternator's regulator is seeing!

Good luck
 

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Seriously,,,,,get back to basics.

There is a possibility that your dash is lying to you.

Load test your battery. A bad battery will 'tell' your alt to kick it up. You have to start at the battery. A battery can show 12v but have a bad cell inside. Load test that same battery and it will die out. If your batter is fine, move to the cables and make sure they are not dropping voltage. 1 little copper strand in that huge cable can carry 12 volts for a meter but it wont carry enough amps to do its job. This is where load test come in. Time to load test the alt. A load test is just what it sounds like, tells the alt to work hard. If the alt kicks it up but you dont see that increase at the battery, look back into the cables.

You need to check the Alt output at the "B+" post on the back of the alt, not just at the battery posts. See exactly what the alt is putting out. Work your way out from there.

If your alt is putting out 17 volts.. your battery is going to expose its guts soon.

If you find a good battery and a good alt, its more than likely in the body harness (fuse box, distribution, buss, gauge, etc) which is a whole new ballgame.

OH, if you have those autozone type, cheezy bolt down aftermarket battery terminals, get rid of them ASAP. They are nothing but trouble.
 

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Discussion Starter · #11 ·
Just an update on the status. My meter has not shown 16-17v of output since that one time. I have had no fluctuation of the needle on the dash meter. However, my battery light is still on.

I have had the battery fully tested, and it is fine. Almost brand new, in fact. Checked the output at the alternator B+ post (only one I could get to without taking skid plate off, and it tests within the proper limits.

I now believe there is a loose/corroded connection somewhere. I am going to start at the battery terminals and work backwards I guess. My Haynes manual wiring diagram is confusing, but I will just have to figure it out, jack the truck up, and just start tracing.

Will report back. Thanks for all the suggestions.
 

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Do you have a load tester? If so, put the positive clamp on the + of the battery and the - on the battery. Load test for 10 seconds. Give it 5 minutes to recover. Then put the positive clamp on the + of the battery and the - on a good frame ground, load test for another 10 seconds. Look for the difference between the two tests which will show any load resistance on the negative cable.
 

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This is an old thread but I'm posting here in case someone else finds it like I did.

2001 Sequoia alternator went out / battery light on / lights dimming / tested bad. Got a new one at Auto Zone - gave me 14.xx volts at the battery posts. Headed out of town on a Boy Scout campout and it died (thanks to frequent jump/drive/jump/drive/repeat, we got there and back).
Took the new A/Z alternator back - they say it tests okay. I say I want my money back anyway and they obliged.
I ordered a new 180 amp alternator from DC Power (good product / horrible service). Installed that and got 12.3 volts at the battery posts / battery light on. Took the DC Power alternator to Auto Zone to test - they say it tests fine. Then I found this thread.

Started measuring voltage & resistance - found weird things. 12.3 volts at the battery posts when running 3.6 volts at the alternator (?). Removed the signal wire from the alternator and it goes up to 6.5 volts (?). Kept looking / testing (re-read this post)...

Aha! The main wire that feeds the relay box looked funny - and loose. Previous owner put a ring terminal under it to power his off road lights. The nut was tight but connection was loose / plastic around it burned / insulation burned. Either there was a short that got hot (probably) or when the original alternator went out, it gave me too much juice (much less likely). I cleaned up the connector & threaded post, added a couple washers so it would tighten when the nut was up on good threads, replaced the bad connector on the off road lights and connected it up on the battery where I can see it. Put it all together and I'm getting 14.6 volts at the battery posts / no battery light / charges fine.

What I learned:
- Listen to the people on this forum - most know what they're talking about. If you've checked everything and someone says, "Why don't you check the connector in the relay box?" just go ahead and check it.
- If everything is working and one part goes bad, that doesn't mean it's the only thing that went bad. Sometimes 2 things can go bad at once.
- Check everything - keep checking - you'll find it.
- When you connect accessories, use good connectors, solder, and shrink wrap. Connect them where they're visible and not hidden & forgotten
- And lastly - no amount of electrical tape will prevent a bad connection from causing problems eventually (remember that previous owner?)

Thanks for the thread / thanks for the forum. I may have never thought to start looking at the wires/connections.
 

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This is an old thread but I'm posting here in case someone else finds it like I did.

2001 Sequoia alternator went out / battery light on / lights dimming / tested bad. Got a new one at Auto Zone - gave me 14.xx volts at the battery posts. Headed out of town on a Boy Scout campout and it died (thanks to frequent jump/drive/jump/drive/repeat, we got there and back).
Took the new A/Z alternator back - they say it tests okay. I say I want my money back anyway and they obliged.
I ordered a new 180 amp alternator from DC Power (good product / horrible service). Installed that and got 12.3 volts at the battery posts / battery light on. Took the DC Power alternator to Auto Zone to test - they say it tests fine. Then I found this thread.

Started measuring voltage & resistance - found weird things. 12.3 volts at the battery posts when running 3.6 volts at the alternator (?). Removed the signal wire from the alternator and it goes up to 6.5 volts (?). Kept looking / testing (re-read this post)...

Aha! The main wire that feeds the relay box looked funny - and loose. Previous owner put a ring terminal under it to power his off road lights. The nut was tight but connection was loose / plastic around it burned / insulation burned. Either there was a short that got hot (probably) or when the original alternator went out, it gave me too much juice (much less likely). I cleaned up the connector & threaded post, added a couple washers so it would tighten when the nut was up on good threads, replaced the bad connector on the off road lights and connected it up on the battery where I can see it. Put it all together and I'm getting 14.6 volts at the battery posts / no battery light / charges fine.

What I learned:
- Listen to the people on this forum - most know what they're talking about. If you've checked everything and someone says, "Why don't you check the connector in the relay box?" just go ahead and check it.
- If everything is working and one part goes bad, that doesn't mean it's the only thing that went bad. Sometimes 2 things can go bad at once.
- Check everything - keep checking - you'll find it.
- When you connect accessories, use good connectors, solder, and shrink wrap. Connect them where they're visible and not hidden & forgotten
- And lastly - no amount of electrical tape will prevent a bad connection from causing problems eventually (remember that previous owner?)

Thanks for the thread / thanks for the forum. I may have never thought to start looking at the wires/connections.
Just to reconfirm this post! I have a 2001 Tundra SR5 4.7L, 190k miles. Just got the frame recall work completed in January. Had a few hiccups since then like the dealer not letting me know the steering rack bushing was shot and it rubbed a hole in the tube. Latest one was what appeared to be the alternator going out. Typical symptoms, no charging, battery light, no voltage increase at the battery while running. It is the original alternator and the battery is actually a 2011 model so I figure it's time for these things to happen. I swapped out everything including the battery to be proactive and still no charging. I checked the alternator connections, voltage across the battery, ground continuity, fuses, everything I could think of... I even took the original alternator that was off to the local Advance for a bench test because I thought the new one I got was faulty...the old alternator was still working!

Turns out the battery cable that connects to the pole in the fuse box was loose, I suppose they disassembled during the frame swap and it didn't get tightened properly and took about a month to wiggle loose. Moral of the story, keep it simple stupid (KISS). Appreciate everyone's suggestions and experiences from this forum. You helped me navigate to the right place. I will just file this one under "preventative maintenance"
 

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Well after spending a full day running through every single thing mentioned in this thread I am stumped. The only thing I can think of is that somehow the bench test (pass) on the old alternator was false AND I got a bad replacement somehow?? Both are Auto Zone Duralast Gold. Brand new battery, also Duralast Gold, shows 12.1 v at this point, battery shows same voltage while truck is running, same voltage at the alternator as well. Testing at the alternator voltage regulator plug end : Getting 12 v on the sensor wire (white) both when truck is off and running, 12 v on the IG wire (black/yellow) only when truck is running and only 10.8 V on the L wire (green/yellow) which as I understand is simply for the gauge and shouldn’t prevent the alternator from sending charge voltage/ current to the battery. Checked all the alternator and battery wiring for corrosion, loose connections etc. checked all fuses with a meter…. 2006 DC 4.7, Any thoughts are gratefully appreciated. Happy Easter 🐇
 

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I have a 2011 Sequoia with 5.7 and 140k miles and teh truck is driven in salt. I have been trying to fix a battery light for over a year now using every post I can find for Tundra/Sequoia charging system light. Voltage at the battery has always been above 14 v no matter how I measure it... between posts, between the positive post and the frame, between the 5a Alt-s and 7.5a Met fuses and negative post... everything looks good. I have replaced the battery and alternator, replaced the serpentine belt, tensioner and idler pulley... all OEM parts and the new alternator is the same 180A. Cleaned up all wire connection and grounds. Removed a mouse nest from the fuse box and fixed a few wires that were chewed up by bypassing the chewed up sections with 18 gauge wire and press clamps. Can't find any more exposed copper in the fuse box, so I don't think there is anything left to fix there. I do wonder if I should revisit my "fixed" wires and solder in new sections instead of using the clamps, but I feel like I'm grasping at straws. My BlueDriver OBD2 scanner has never detected any codes. The Control Module Voltage reportd by BlueDriver is 13.57v while the voltmeter shows 14.62v at the battery. Is this the reason the battery light is on? Any ideas out there?

Oh yea, there are no add on accessories, this is a stock set up.
 
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