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Discussion Starter #1
I will start off with the details:
- 2007 AT 4x4​
- 112k miles​
- Battery is Odyssey 34R-PC1500T AGM Group 34 installed brand new about 7 months ago​
- Alternator is stock Denso Remanufactured 100 amp installed about 2 months ago​
- HKB Electronics Alternator Voltage Booster installed about a month ago​

Here is the problem:

My OEM battery finally bit the dust on the last day at Summit XI last year, so I replaced it as soon as I got home with a nice new Odyssey AGM battery and everything seemed to be okay. Then, a few months later, the alternator started making a terrible sound out of the blue and it was putting out little to no charging voltage. I replaced the alternator with a Denso remanufactured 100 amp unit and it seemed to work okay at first.

Shortly after that, I noticed that after the engine warms up, the voltage will fluctuate all over from 13-14 volts at idle or at low RPM. When the truck is in gear and moving, the voltage seems to sit comfortably between 14.5-14.7 volts, but when coming to a stop/sitting stopped, switching gears to reverse, neutral or park, and the voltage starts fluctuating again and the headlights and dash lights dim noticeably with the fluctuations.

I ran an OBDII scanner to make sure it wasn't just the gauge and I also tested with a multimeter. I am not running any crazy aftermarket accessories, and I only have one small LED light wired up which is rarely used. I don't have the heater or AC running and the temp dial is resting in the middle, so really the only electrical draw I would have are the DRL's and the stock stereo, so nothing that would be causing a huge drain. The battery also stays charged over the weekend without driving it, so it doesn't seem like there is any significant parasitic draw, although I have not tested thoroughly yet.

I know the voltage is supposed to fluctuate a little, but I never had this problem until installing the new alternator. Could the problem be a faulty remanufactured alternator, or should I be looking at something else? Also, just to note, the problem was happening before the HKB Alternator Booster was installed, it just fluctuates at a slightly higher voltage range now.

Thanks in advance for any and all help/advice.
 

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I just replaced a one year old Denso remanufactured alternator this weekend.

Symptoms started the same, dimming headlights became popping sounds on the radio with sudden breaking, headlights turned on... The final was on the Hwy turned on the headlights and the ignition turned off, cycled back on - twice.

I took the alternator back to Oriellys for lifetime warranty replacement. It passes their 'exhaustive' 8 second test, the only report information provided is PASS. No voltage ranges, amperage, voltage drops at load... just PASS. Not wanting to put the same unit back in, I kept my core, purchased another alternator and installed it. No more dimming, radio pop sounds, stalling... fixed.

A call to Orielly's Corporate Office and they honored the lifetime warranty. I can now replace an alternator pretty quickly which I wouldn't bet against happening again in the next couple of years. :|
 

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Discussion Starter #4 (Edited)


Thanks! I read that thread while doing some research, but nothing stood out to me. After re-reading it though, it could be that my AGM battery is not charged all the way and would keep causing dips at low rpm because it wants a higher voltage. I measured the battery after having sat all day and it came in at 12.8 volts. Not sure if that is in the healthy range for the battery but I will do some poking around for info. I did drive it a few times while the alternator was dying and noticed the voltage started reading pretty low, so maybe I drained the battery too much and the alternator can’t recharge it all the way. Maybe I will try putting it on a trickle charger.

I checked around on the Odyssey website and found some info on a brochure for the Extreme Series batteries. It says "If the ODYSSEY Extreme Series battery’s voltage is 12.65V or greater, simply install the battery in your vehicle and you are ready to go!"
brochure
So it looks like 12.65V is the low end of healthy for the resting voltage.
 

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Discussion Starter #5
I just replaced a one year old Denso remanufactured alternator this weekend.



Symptoms started the same, dimming headlights became popping sounds on the radio with sudden breaking, headlights turned on... The final was on the Hwy turned on the headlights and the ignition turned off, cycled back on - twice.



I took the alternator back to Oriellys for lifetime warranty replacement. It passes their 'exhaustive' 8 second test, the only report information provided is PASS. No voltage ranges, amperage, voltage drops at load... just PASS. Not wanting to put the same unit back in, I kept my core, purchased another alternator and installed it. No more dimming, radio pop sounds, stalling... fixed.



A call to Orielly's Corporate Office and they honored the lifetime warranty. I can now replace an alternator pretty quickly which I wouldn't bet against happening again in the next couple of years. :|


Dang, that doesn’t sound good! I’m glad Orielly’s came through and you got your problem fixed though. I got my remanufactured alternator from RockAuto and they are pretty good about warranties and exchanges. I haven’t noticed any noise on the stereo and it hasn’t stalled yet, thankfully. Maybe I will just go ahead and exchange it just for good measure. Thanks for the input!
 

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The Denso remans are crap. Send it back. I bought one for a 99 4runner on my kids truck and it died quick. In fact the voltage reg allowed the voltage to rise above 16v and almost toasted my wiring. Lost dash lights while driving. They check the parts and if they check okay the don't replace them The voltage regulator is a costly part and when it heats up, starts failing. Get a low mileage 4runner 130A alt from ebay. Just bought one for $60 shipped and its OEM working.
 

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Discussion Starter #7
I was debating getting one of the high output alternators at first, but I thought it would be better to get as close to stock as possible. Looks like it may have been worth it after all. What year is your FJ and what year 4R was the alternator from? It looks like the 05-15 Tacoma Tow Package alternator will fit the FJ, and the 2010+ 4R alternators fit the 2010+ FJs according to this thread: 130 amp alternator all model fj
 

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I was debating getting one of the high output alternators at first, but I thought it would be better to get as close to stock as possible. Looks like it may have been worth it after all. What year is your FJ and what year 4R was the alternator from? It looks like the 05-15 Tacoma Tow Package alternator will fit the FJ, and the 2010+ 4R alternators fit the 2010+ FJs according to this thread: 130 amp alternator all model fj
http://www.fjcruiserforums.com/forums/stereo-electronics-electrical/691553-130-amp-alternator-all-model-fj.html

Mine is 2007 FJC
 

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Voltage regulator
Alternator
Poor connections

From your explanation I would guess your VR is giving your Alt a set point and at lower RPM your Alt is not reacting as normal

Connections are easy to check and your grounds are very important

Your add on resistor to raise your voltage for your Odessy could cause this also if you had a loose connection there
 

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Discussion Starter #10
Voltage regulator
Alternator
Poor connections

From your explanation I would guess your VR is giving your Alt a set point and at lower RPM your Alt is not reacting as normal

Connections are easy to check and your grounds are very important

Your add on resistor to raise your voltage for your Odessy could cause this also if you had a loose connection there

I could double check the connections, but having just recently put the new battery in, I cleaned all the terminals and tightened connections but I guess anything is possible and it’s definitely worth checking.

I also double checked the voltage booster by switching it out with the stock fuse and I still got the same fluctuations, just at a lower voltage.

I ordered a replacement under the warranty for the alternator so I will see if that fixes it. If not, I will probably try to return it and get a Tacoma or 4Runner high output alternator and hopefully that will be the end of it.
 

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Discussion Starter #11
Update:

I got a second remanufactured Denso 100 amp alternator through warranty and installed it last night. I thoroughly cleaned all connections and made sure everything was tight. Much to my dismay, however, I still have the same problem with the voltage fluctuating wildly and the lights dimming at idle. It could be that I got two alternators with bad voltage regulators, but I am starting to think it may be something else.

Could it be that trying to charge the Odyssey battery is too much strain on the baby 100 amp alt? Has anyone else ever had a problem with that?

I am going to try cleaning the MAF and Throttle Body and see if that helps at all. It seems like that is a magic cure for many symptoms.

If that doesn’t work, my next attempt will be to get a used OEM 130 amp alt from a Tacoma or 4 Runner and see if that helps at all.

With plenty of other maintenance things quickly piling up, I would really like to have this settled -_-
 

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Check the continuity of all 4 wires on the alternator plug. If the charge wire is broken the alternator will stay in high output and toast your wiring. Had it happen on our 4Runner. I rewired the sensor wire and the problem resolved

 

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Discussion Starter #13
I will try that tonight when I get home. How difficult was it to re-wire the harness?
 

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Check the continuity of all 4 wires on the alternator plug. If the charge wire is broken the alternator will stay in high output and toast your wiring. Had it happen on our 4Runner. I rewired the sensor wire and the problem resolved


+1 for the pic, thanks! I’ll have to dig through my copy of the electrical wiring diagram and get an idea of what I am looking at. I popped off the harness tonight and mine only has 3 wires...? In the service manual (please excuse my terrible markup) it shows S, IG and L wires for the harness and the B+ that goes from the alternator stud to the battery.

Forgive my electrical noob ignorance, but did you test the charge wire (yellow/green wire) at the harness and the 7.5 amp Charge fuse for continuity or somewhere else? Sorry, I’m still trying to get all this electrical stuff down. Thanks for all the help, I really appreciate it!

 

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OP, did you ever find a resolution to this? I installed a reman 130A Denso from Rockauto about 8 months ago, and now my voltage is fluctuating at idle.
 

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OP, did you ever find a resolution to this? I installed a reman 130A Denso from Rockauto about 8 months ago, and now my voltage is fluctuating at idle.


Nope, I am still having the same issues. I haven’t been able to mess with it for a while now because I have been so busy with work. I think I might just take it in somewhere and try to get it sorted out though.

Did you notice the problem right away, or did it just start doing it out of nowhere? Also, what kind of battery are you using?
 

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Nope, I am still having the same issues. I haven’t been able to mess with it for a while now because I have been so busy with work. I think I might just take it in somewhere and try to get it sorted out though.

Did you notice the problem right away, or did it just start doing it out of nowhere? Also, what kind of battery are you using?
I just noticed it this week. If it were doing it before, then it must have been more subtle. Now the fluctuations are visible on the dash battery gauge. The battery is a 3-year-old Duralast that it came with.
 

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(snip) If the charge wire is broken the alternator will stay in high output and toast your wiring.
This is incorrect.

If the alternator's voltage sensing line (terminal S) is disconnected from the battery, the alternator's internal voltage regulator TURNS OFF all alternator output, and TURNS ON the charging warning light on the instrument panel.

The Denso alternators used in FJs have an internal solid-state voltage regulator. They use a separate voltage sensing line tied directly to the battery's + terminal to accurately "read" the battery voltage, and to adjust alternator output current to achieve the target battery voltage. This allows the voltage regulator to maintain the correct voltage at the battery regardless of any resistance (voltage drop) in the alternator's high-current output line, which is also tied to the battery + terminal.

This voltage sensing line is where you can insert a silicon diode to induce ~1V voltage drop, and thereby "trick" the alternator into boosting its output voltage by ~1V to fully charge an AGM battery.

The graphic below is Toyota's explanation of how disconnecting the alternator's voltage sense line (terminal "S") shuts down the alternator, and shows more detail of the alternator's internal circuitry. Transistor TR1 is the "switch" that controls current to the alternator rotor. Turning this transistor on and off is how the alternator regulates current output. When TR1 is turned off, there is no output from the alternator. (Click on the image for a larger, higher resolution version.)

OP, all the evidence you have provided so far indicates that you have a fault in the alternator wiring, high resistance at the battery terminal clamps, or a bad ground at the battery or somewhere else in the charging system. Denso alternators are very reliable, and there is no evidence that you have a faulty alternator.

1. Very thoroughly inspect ALL of the alternator-related wiring, especially the contacts in the connector that plug into the alternator. Each contact must be bright and clean, free from any corrosion, and must firmly grip the contact pins in the alternator.

2. Remove both of the battery terminal clamps, and clean them and the battery terminals with a wire brush to a bright, clean, bare-metal condition, and then re-clamp firmly.

3. Temporarily replace your voltage-boosting diode with a regular 7.5A fuse to eliminate that as a suspect.

4. Make sure that engine block and battery negative terminal grounds are clean and bright at the body ground points; remove the bolts, clean the lugs and sheet-metal contact areas with a wire brush, and properly re-tighten the bolts.

5. Make sure the contacts in the fuse box for the 7.5A ALT fuse are clean and bright.

6. There is a very small possibility that your AGM battery is defective, and has an intermittent in the internal cell-to-cell connection straps. However, this will usually manifest itself as a cranking problem when starting, when there is the highest current draw.
 

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Update:

I got a second remanufactured Denso 100 amp alternator through warranty and installed it last night. I thoroughly cleaned all connections and made sure everything was tight. Much to my dismay, however, I still have the same problem with the voltage fluctuating wildly and the lights dimming at idle. It could be that I got two alternators with bad voltage regulators, but I am starting to think it may be something else.

Could it be that trying to charge the Odyssey battery is too much strain on the baby 100 amp alt? Has anyone else ever had a problem with that?

I am going to try cleaning the MAF and Throttle Body and see if that helps at all. It seems like that is a magic cure for many symptoms.

If that doesn’t work, my next attempt will be to get a used OEM 130 amp alt from a Tacoma or 4 Runner and see if that helps at all.

With plenty of other maintenance things quickly piling up, I would really like to have this settled -_-
F-YAY -

You are not using a logical failure analysis process, and are not identifying a probable root cause for your electrical system problem.

If you see sudden, LARGE swings in system voltage, you have either an intermittent OPEN circuit, or an intermittent SHORT circuit in the BATTERY circuit, not an alternator problem.

The battery is a huge reservoir of electrical energy. If all the connections to the battery are good, and the battery itself is good, and charged, system voltage CANNOT suddenly change dramatically. It can slowly increase over a period of many minutes as the battery charges, or slowly decrease over a period of many minutes as the battery discharges, but it cannot instantaneously change unless there is an intermittent open or high-current short.

A high-current short will usually be detectable by smoke, burned insulation smell, and obvious overheating of the insulation on the wiring where the short occurs. Toyota does a good job of protecting OEM circuitry with fuses, so a typical high-current short can only exist for a few seconds before the fuse opens and halts current flow.

Have you seen any evidence of a repeated, intermittent high-current short circuit?

If not, the next condition to look for is an intermittent open (or intermittent high-resistance) condition in the battery B+ or ground circuits. First, disconnect the terminal clamps from the battery terminals and wire-brush everything to bright, clean metal and and then re-connect everything.

Disconnect the main battery ground connection at the inner fender liner, wire-brush all contact surfaces to a bright-metal condition, and re-connect.

If the problem persists, you may need to disassemble the engine-bay fuse-box and make sure that all the connections to the main B+ buss are clean and tight.

You stated that the lights dim at idle; the assumption is that they brighten up as engine RPM is increased. This is proof that your alternator IS providing an output, and that for some reason your battery voltage is low, or there is high resistance in the battery circuit, so it cannot provide enough current to maintain a system voltage of 12V or more UNTIL the alternator picks up the load at higher RPM.

The standard alternator is perfectly capable of fully charging your Odyssey AGM battery, especially if you are using a fully-functional voltage-boost diode.

Speaking of the voltage-boost diode, is yours the type that contains DUAL diodes, and can be installed in the fuse box in any orientation, or is it the less-expensive SINGLE diode type that MUST be correctly oriented so the diode polarity allows current to flow to the alternator's voltage sensing line?

As you have surmised, the probability sequentially getting two defective alternators is extremely low.

Cleaning your MAF and throttle body and hoping that will "cure" an electrical problem is (of course) ludicrous.

Likewise, installing a 130A alternator will have absolutely no effect because your problem is NOT with your electrical system loads continuously drawing more than the 100A that the stock alternator can supply.

You have some other electrical fault in the battery, or battery wiring and grounding, and NOT an alternator problem.
 

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The battery is a huge reservoir of electrical energy. If all the connections to the battery are good, and the battery itself is good, and charged, system voltage CANNOT suddenly change dramatically. It can slowly increase over a period of many minutes as the battery charges, or slowly decrease over a period of many minutes as the battery discharges, but it cannot instantaneously change unless there is an intermittent open or high-current short.
If the OP's voltage fluctuations are anything like the ones I'm seeing, they are not exactly dramatic. It bounces around between 13.1v and 13.6v, as measured at the battery terminals. Below is a short video of the dash battery gauge at idle.

https://youtu.be/UzKHrXyBzss
 
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