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Discussion Starter · #1 ·
Longtime lurker, first time poster so I'm just going to get this started, sorry for the length. Here's a taste, --Transmission Fluid In Wiring Harness-- and a squirrel, and then some.

08 FJ / 213,183-miles / Automatic

Noticed an uptick in fuel consumption lately, ended up throwing codes for the following,
-P0171 -P2A00 -P0138 -P0101

For some reason I had a feeling the problem was electrical so I took it to the dealership. They diagnosed as a bad AF Sensor, Bank 1, Sensor 1, and proceeded to fix.

But the next day the same codes got thrown, gas consumption was up still, and I was concerned seeing as how I had barely driven 50 miles since the "fix"

So they took the car back and that's where things got weird.

The tech could NOT figure out why the codes kept tripping or why the OEM parts where causing incorrect voltages, the AF sensor, bank 1, sensor 1 would run at 3.3-7+V when it's supposed to sit steady at 3.0V

This video here is basically the first diagnosis, thinking it was only the sensor that was bad: https://tvin.s3-accelerate.amazonaws.com/d5e5437ab539dad89cbd95979bb99ae2.mp4?t=1656025449440

Then they swapped in the aftermarket one I had in originally and surprisingly things were fine voltage wise.... until you got on the gas and voltages would go out of range, 3.7+V on the AF sensor b1, s1, again. They even pulled a techs OEM sensor out of his FJ and swapped that in, and it still had the same problem as the other OEM part and they couldn't figure it out.

They also put in new spark plugs and o2 sensors in at this point.

-would like to add that the car drove and worked fine at this point, minus the extra gas consumed with faulty sensor-


So that's when they dug deeper......

After 2-3 weeks they sent this video.

^The Toyota dealership I took it to ended up contacting Toyota directly and brought this all the way up to Toyotas Engineering Division and their response after 2 weeks was basically sorry, this is a completely unique issue we've never seen before, and were unable to diagnose further.

And so, what they are saying is, well the tech at the dealership at least, was that they found trans fluid in every connector plugged into the ECU, and that transmission fluid is "somehow" being fed through the Main Engine Harness, the Transmission Harness, and the Front Door Harness, and being pushed into the ECU causing shorts across the board. See below for example of codes caused by the shorts, as well as, see second video above for example of what connectors are affected.

I brought it in with those 4 codes above and now it's come back with the following,
-P2716 -P0778 -P0748 -P0222 -P2759 -P2610 -P0986 -P0971-P0974 -P2743 -P0713 -P0171 -P0977, runs like ****, sounds like ****, zero acceleration, literally much more broken then how I brought it in, I've never seen it drive or operate like this.

They said to fix it would require a new harness for each listed above, as well as a new ECU as more and more fluid has been pushed into it, which they say is now causing all these new codes AND shorts, which is causing the car to barely run, which is a new thing as it was great before I brought it in. smh.

So please for the love of all things good in the world,

Has anyone else had this problem before???!? Or how the hell this could of even happened?? I can't find anything on it and Toyota themselves said it was unique and I don't know what to do I love my car I don't want to lose it I'd do anything!

Maybe some techniques on cleaning the harnesses and trying to salvage them? And only getting a new ECU idk?

Or anybody parting out an old FJ... I could use some harnesses and an ECU:LOL::cry:

Any ideas would be appreciated!!

Sorry for the video links the files were to big to upload, if the individual ones don't work then the main one below, which has all 3 videos works as well, you just have to scroll between videos 1 and 3 on the page while ignoring video 2 as it has no sound/issues while recording. 910167 -not sure why it's shortening the link to this

and yes the link above contain my name, either said outloud or displayed on the page but so does my profile so please try to ignore that I'm desperate lol

tl;dr -Transmission fluid is "somehow" being fed through the Main Engine Harness, the Transmission Harness, and the Front Door Harness, and being pushed into the ECU causing shorts across the board and major damage to all systems associated. Quoted me about 10k usa buckaroos to fix my poor thing so any outside help would be much loved!

Again sorry for the length hopefully some of y'all have hung on until the end and can help!!
 

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Maybe the transmission case vent is blocked or clogged causing the built up pressure from heat and expansion, is forcing ATF to be pushed up the valve body solenoid wires and through the harness?
 

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I'm not buying the hypothesis that ATF by itself is "shorting out" anything.

ATF (regardless if mineral oil base or synthetic) is an excellent electrical insulator ... think of the seven solenoids continuously operating in 200 degree ATF in the transmission pan, or the oil-filled HV transformer on the pole half a block from your house.

The fact that they are claiming that they can't get any repeatable electrical resistance measurements minute by minute or day by day tells me something else is going on. The technician narrating the video clips doesn't come across as someone who is skilled in electrical/electronic troubleshooting.

And, the comment about "the things they replaced just to rule things out" is shocking ... they're just blindly replacing parts, hoping that eventually they'll stumble on the real root cause of the problem.
 

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This is a not unheard of issue with high mileage vehicles. Toyota does know about it. Several instances on the 4Runner forums.

The internal transmission solenoid harness is weeping oil through the external electrical plug. Via capillary action, transmission fluid is migrating through the connector, up the harness to the main ECU in the upper right kick panel. From there, it goes down into the main engine harness and to the O2 sensors which causes the driveability problems. (To check for the issue, simply unplug the harnesses at the ECU and see if there is oil present in the connectors).

I forgot how much the internal trans harness was, but I think it was under a hundred bucks. Replacement engine harnesses are very expensive, but still available last time I checked.
 

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Not gonna lie, never heard of that… on any car…. But I’m no means an expert, check out hollanderparts.com, they’ve got a ton of fj’s at salvage yards on there and I bet you could find what you’re looking for on some of them. Sounds like fireball knows what he’s talking about, so I’m just gonna go out on a limb and say listen to him hahahaha sorry this is happening to ya man
 
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I have a spare main engine harness ( from a 2006 Tacoma). I used the engine, but the harness is in very good condition. If you can confirm it fits your FJ, which I believe it will, we can work out a friendly deal on it.

I also have a spare 07 4x4 AT ECU, but I'd really prefer to hold on to that. Let me know if I can help.

Also, in addition to confirming the status of the harness, double check battery voltage and charging voltage under load. Low battery voltage on these vehicle can certainly cause a multitude of symptoms and codes. I always like to sort out the basics first. Check your battery terminal for corrosion and all your chassis grounds.
 

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It's been known to happen in the old Supras. The culprit there was the cam position sensor leaking engine oil into the harness. Instances can be found in Mercedes, Porsche, and Mopar forums of similar harness oil wicking issues.

If your ECU circuit boards have been damaged by the additives in the trans fluid, it will need to be replaced. The internal trans harness MUST be replaced or the problem will recur. The remaining wiring harnesses can hopefully be salvaged once that has been done. The wicking occurs slowly, so you need to repeatedly monitor the ecu plugs for oil and clean them to prevent your new ECU from damage. Some people unwind 6 inches of tape from the harness in some strategic spots for monitoring and cleaning until the existing oil in the harness clears and stops wicking.
 
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That tech does not know how to troubleshoot electrical issues. Rodent nest found and he blames transmission fluid in the ECU, fix the transmission soleniod and internal harness. Clean the rest. You have a electrical issue that is causing the problem elsewhere. The trans fluid on the ECU is a secondary issue.
 
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I'm not buying the hypothesis that ATF by itself is "shorting out" anything.

ATF (regardless if mineral oil base or synthetic) is an excellent electrical insulator ... think of the seven solenoids continuously operating in 200 degree ATF in the transmission pan, or the oil-filled HV transformer on the pole half a block from your house.

The fact that they are claiming that they can't get any repeatable electrical resistance measurements minute by minute or day by day tells me something else is going on. The technician narrating the video clips doesn't come across as someone who is skilled in electrical/electronic troubleshooting.

And, the comment about "the things they replaced just to rule things out" is shocking ... they're just blindly replacing parts, hoping that eventually they'll stumble on the real root cause of the problem.
Yeah agreed with FJtest and Glenarch, in not buying the ATF causing electrical issues theory, look at this study by SAE:
ATFs "can be considered insulators with the ability to dissipate static charge.", and even safe to use in electric vehicles.
 

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Yeah agreed with FJtest and Glenarch, in not buying the ATF causing electrical issues theory, look at this study by SAE:
ATFs "can be considered insulators with the ability to dissipate static charge.", and even safe to use in electric vehicles.
There is no question that under some conditions, individual wires within wiring harnesses can become conduits for carrying fluids far from their original sources. Some Volkswagen models had problems with engine coolant slowly seeping through engine bay wiring and eventually contaminating the engine ECM in the passenger compartment, and in some cases making it as far as the tail lights.

The root cause ended up being a defect in the coolant level sensor in the pressurized engine coolant reservoir. The electrical connector to the sensor was well sealed, and when the sensor developed an internal fluid leak, the pressurized coolant leaked out of the sensor housing at the electrical contacts, into the sealed connector, into the wiring harness, and finally into the main body wiring harness. However, the fluid involved was engine coolant (50% water), and that is far more conductive than any mineral oil should be.

After some additional thought about the ability of ATF to cause electrical 'shorting' at ECM connectors, I remembered that WS fluid supposedly has some hygroscopic characteristics; I don't know if this is any different than any other type of ATF. Regardless, if WS ATF can absorb some moisture, and this moisture content can cause some low-level conductivity (and leakage current between closely-spaced connector pins), then ATF contamination at the ECM could cause problems with low-level signals, like the signals from the air-fuel and O2 sensors.
 

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Discussion Starter · #12 ·
I'm not buying the hypothesis that ATF by itself is "shorting out" anything.

ATF (regardless if mineral oil base or synthetic) is an excellent electrical insulator ... think of the seven solenoids continuously operating in 200 degree ATF in the transmission pan, or the oil-filled HV transformer on the pole half a block from your house.

The fact that they are claiming that they can't get any repeatable electrical resistance measurements minute by minute or day by day tells me something else is going on. The technician narrating the video clips doesn't come across as someone who is skilled in electrical/electronic troubleshooting.

And, the comment about "the things they replaced just to rule things out" is shocking ... they're just blindly replacing parts, hoping that eventually they'll stumble on the real root cause of the problem.

Yeah I wasn't to confidant when they were starting to say they just dug into random things. I can post pics in a bit, I see the fluid dripping from the bottom of the wires of the main part going into the ECU so I know there is an issue with liquid and the wiring there, maybe they are wrong about the type of fluid and it isn't trans. The second video does go into more detail with what connectors and where everything is happening, first one was just diagnostics but thank you for your reply
 

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Discussion Starter · #13 ·
This is a not unheard of issue with high mileage vehicles. Toyota does know about it. Several instances on the 4Runner forums.

The internal transmission solenoid harness is weeping oil through the external electrical plug. Via capillary action, transmission fluid is migrating through the connector, up the harness to the main ECU in the upper right kick panel. From there, it goes down into the main engine harness and to the O2 sensors which causes the driveability problems. (To check for the issue, simply unplug the harnesses at the ECU and see if there is oil present in the connectors).

I forgot how much the internal trans harness was, but I think it was under a hundred bucks. Replacement engine harnesses are very expensive, but still available last time I checked.
I must be lacking in my google skills cause I couldn't find anything!! Thank you so much for this info it'll definitely help me narrow down where to look and how to go about it, I greatly appreciate your input!
 

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Discussion Starter · #14 ·
Not gonna lie, never heard of that… on any car…. But I’m no means an expert, check out hollanderparts.com, they’ve got a ton of fj’s at salvage yards on there and I bet you could find what you’re looking for on some of them. Sounds like fireball knows what he’s talking about, so I’m just gonna go out on a limb and say listen to him hahahaha sorry this is happening to ya man
That site kept popping up when I was trying to source some parts and I was hesitant but upon your suggestion I'll have to give them another look, thanks for the info!
 

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Discussion Starter · #15 ·
I have a spare main engine harness ( from a 2006 Tacoma). I used the engine, but the harness is in very good condition. If you can confirm it fits your FJ, which I believe it will, we can work out a friendly deal on it.

I also have a spare 07 4x4 AT ECU, but I'd really prefer to hold on to that. Let me know if I can help.

Also, in addition to confirming the status of the harness, double check battery voltage and charging voltage under load. Low battery voltage on these vehicle can certainly cause a multitude of symptoms and codes. I always like to sort out the basics first. Check your battery terminal for corrosion and all your chassis grounds.
Oh my god if it matches my code of "82111-35C20" then I'll do whatever I have to for that harness!! I've sourced about every other thing I listed rather inexpensively for oem parts, except the harness and the ecu!

I have a lead on an ecu already so I wont heckle you for that but I haven't had much luck on a harness that isn't $1,800+ and I just don't have that kind of cash right now but I am up for working something out with ya so please let me know!

I took a look at the wiring at the ecu, and along the main engine harness last night and saw fluid only in connectors that were plugged into the ecu itself, yet there was a pool of fluid at the base of the main group of wires, like right at the bend where they turn upwards. Voltages were good at battery and connections were solid but I have had issues with slight fluctuations in the meter in the past so I'm usually pretty good about battery health! Although it's always worth a double check.

Thank you I appreciate your time!
 

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Discussion Starter · #16 ·
It's been known to happen in the old Supras. The culprit there was the cam position sensor leaking engine oil into the harness. Instances can be found in Mercedes, Porsche, and Mopar forums of similar harness oil wicking issues.

If your ECU circuit boards have been damaged by the additives in the trans fluid, it will need to be replaced. The internal trans harness MUST be replaced or the problem will recur. The remaining wiring harnesses can hopefully be salvaged once that has been done. The wicking occurs slowly, so you need to repeatedly monitor the ecu plugs for oil and clean them to prevent your new ECU from damage. Some people unwind 6 inches of tape from the harness in some strategic spots for monitoring and cleaning until the existing oil in the harness clears and stops wicking.
Amazing reply I'll add it to my notes, thank you!

So you're saying I can potentially salvage some of the wiring? I was wondering about just cleaning the connectors but the fluid is actually inside the wiring? Cause current plan is buying a front door RH harness, main engine harness, and a trans harness, so if I could save by reusing old parts I'd be way down for that but having never encountered this issue I had no idea how to remedy.

Where the ecu is in FJ I can't imagine anything there would drip per se, but yeah it's fried with all those codes it's giving, currently trying to source a new one, seeing like $668 lowest for an oem one that's not ebay.

Also sourced an oem internal trans harness for only $73 so that's absolutely in the plans to do, gotta get a trans pan gasket with that but that's fine. And yeah even after replacing all that I'm planning on keeping and eye out on it now that I know it's a thing cause I can't/wont go through this again lol

Again thank you for your time!
 

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Discussion Starter · #17 ·
That tech does not know how to troubleshoot electrical issues. Rodent nest found and he blames transmission fluid in the ECU, fix the transmission soleniod and internal harness. Clean the rest. You have a electrical issue that is causing the problem elsewhere. The trans fluid on the ECU is a secondary issue.
Yeah I was kind of annoyed when he focused so much on the rodent as that lil bugger had been long gone, and I never saw any bites or chewing/claw marks so obviously wasn't there long.

Maybe didn't want to do it idk, I don't wanna assume the worst. The parts they quoted me weren't far off from the outside market but after labor they wanted more than 10k was like no dude hell noooo

But anyways thanks for your response I will add it to my notes, thank you for taking the time!
 

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Discussion Starter · #19 ·
There is no question that under some conditions, individual wires within wiring harnesses can become conduits for carrying fluids far from their original sources. Some Volkswagen models had problems with engine coolant slowly seeping through engine bay wiring and eventually contaminating the engine ECM in the passenger compartment, and in some cases making it as far as the tail lights.

The root cause ended up being a defect in the coolant level sensor in the pressurized engine coolant reservoir. The electrical connector to the sensor was well sealed, and when the sensor developed an internal fluid leak, the pressurized coolant leaked out of the sensor housing at the electrical contacts, into the sealed connector, into the wiring harness, and finally into the main body wiring harness. However, the fluid involved was engine coolant (50% water), and that is far more conductive than any mineral oil should be.

After some additional thought about the ability of ATF to cause electrical 'shorting' at ECM connectors, I remembered that WS fluid supposedly has some hygroscopic characteristics; I don't know if this is any different than any other type of ATF. Regardless, if WS ATF can absorb some moisture, and this moisture content can cause some low-level conductivity (and leakage current between closely-spaced connector pins), then ATF contamination at the ECM could cause problems with low-level signals, like the signals from the air-fuel and O2 sensors.
Informative and hits all the gaps I had been wondering! I thought for sure there was no way in the tiny space that is a wire, that there was enough room for any fluid to pass through but after reading your reply and all the the others it sounds like there is some pretty empirical evidence in the matter. Unfortunately I might add lol

Love your thought at the end excellent observation. I feel like in the most critical of circumstances I could see that issue developing in such a minute, but problematic manner, in the way in which you describe but what are the odds!!

Appreciate you taking the time
 

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Oh my god if it matches my code of "82111-35C20" then I'll do whatever I have to for that harness!! I've sourced about every other thing I listed rather inexpensively for oem parts, except the harness and the ecu!

I have a lead on an ecu already so I wont heckle you for that but I haven't had much luck on a harness that isn't $1,800+ and I just don't have that kind of cash right now but I am up for working something out with ya so please let me know!

I took a look at the wiring at the ecu, and along the main engine harness last night and saw fluid only in connectors that were plugged into the ecu itself, yet there was a pool of fluid at the base of the main group of wires, like right at the bend where they turn upwards. Voltages were good at battery and connections were solid but I have had issues with slight fluctuations in the meter in the past so I'm usually pretty good about battery health! Although it's always worth a double check.

Thank you I appreciate your time!
well, this is disappointing, it looks like the part number is 82121-04490.

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