Just out of curiosity have you pulled the transmission sensor connector off to check it? just curious if its completely saturated with fluid and then we definitely know that's where its coming from as the source instead of something else?

No I haven't. There are a few on or near the transmission I need to check.

I am out of town for the weekend, but before I left I pulled the same connectors and blew them our with my air compressor. The amount of fluid that came out of a few of the ecm connectors was really remarkable.

I didn't get any time to work on it like I wanted either. I will keep you posted when I can get it up on a lift and take a look at all the connectors I can find.

I cleaned out my ECU connectors again with Electronic Cleaner and let it dry out really good... mine isn't completely saturated, but its got a lot of fluid in there for sure...

The light stayed off while on the highway, but as soon as I got off it did come back on. Need to locate the transmission sensor next and inspect it.

I also noticed from the below link, that he spliced in solid wire into both downstream 02 sensors after replacing with new. Doesn't mention anything about replacing the trans sensor, or even what happens to the fluid by the ECM. Wish there was a way to contact the owner.

https://www.justanswer.com/toyota/6x...r-chronic.html

"Just wanted to post an update:

I think I have a solution to the A/F sensors failing. I am now pretty confident that the problem was transmission fluid wicking through the wiring harness from the transmission sensor to A/F sensors (including between connectors in the ECM behind the glove box). I replaced the failed A/F sensors with new sensors, but before I installed them I spliced in a piece of solid wire in each of the four conductors. The theory was that this would block the transmission fluid that was wicking through the braided wire. I did this about 1.5 years ago and have not had a problem since. Prior to this fix, the A/F sensors were failing in just a few weeks after installing. I also preformed this fix to one of the downstream O2 sensors that failed. I used high quality sealed but splices to splice in the solid wire segments (http://www.mcmaster.com/#9895k11/=tbr293)."

This seems to be the sensor;

https://www.justanswer.com/toyota/80...nner-took.html

https://parts.lakelandtoyota.com/p/_...212560310.html

Haven't had too much time to dig into this more. I did find home Depot sells bulk solid wire, so I bought a few feet of the smallest gauge (think it was 18).

The code that keeps coming up lately after I cleaned all of the plugs out is p0136, downstream bank 1. You can see from the tq app, there is no signal. I'll probably start here with splicing in the solid wire. Note that I have never been able to get an upstream graph to work with tq.

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Does anyone have any pictures of the wires that people are splicing in to wick the fluid away? I pulled my connectors Thursday night and sure enough the second plug from the top did have transmission fluid residue on it. I cleaned all 5 with CRC electrical cleaner and Knock on wood the light has not come back on. I surly hope I have narrowed this issue down. I will splice wires in to negate the oil transfer as I love this truck but it has been driving me crazy for the past 6 months.

Did you pull the plugs from the 02 sensors just to verify those were saturated?

I haven't gotten around to splicing yet, but I'll take a few pics when I do. I think @BoostinZX was going to splice his too.

Cleaned all the connectors and the light stayed off for about 50 miles and it is back on. How hard is it to replace the wiring harness in this truck? I think it has to be narrowed down to a bad ECU or faulty wiring harness. I really don't know what else it could be.

Have you verified the 02 connectors have fluid in them?

Doubtful it is the ECU. Got to stop the fluid capillary flow. I plan to look more into this when I get more time in a few weeks.

So now I am getting a P2238 code (upstream bank 1 sensor 1). I plan to pull the connector over the weekend. Anticipating it is fluid filled as well.

"P2238 is an OBD-II generic code for the engine control module (ECM) detecting the O2 sensor for bank 1 sensor 1 has a short circuit for the heater control circuit of the O2 sensor."

"The wiring or connector for the O2 sensor has a short circuit or corrosion in the connections."

sorry this is so delayed. (I didn't realize you guys had kept this alive until I got an email update about a PM this morning)

This has to be one of the oddest things I've encountered in my time wrenching.
I've been fighting this with no good solution.

Typically my CEL would come on, along with VSC etc.
When I pull the codes they indicate the one or both rear 02 sensors
Knowing the situation with my car and the fluid wicking…

I change my 02 sensors (both rears) and spray electrical cleaner in the ECU connectors under the glove box.

Then i reset the check engine light, and also do a zero point calibration (to eliminate the VSC stuff).

This process usually last me about a year, and I can get o2 sensors for under 100 online each.


But I have changed my approach a bit this last time. Instead of OEM style 02 sensors I used Bosch universal fit sensors bc they create another connection point for the fluid to have to pass through (effectively another plug in the system). I don't know if this will help or not… I've only been running this way for about a month.



My last ditch thought was to re-pin the entire 02 circuit from sensor to ECU to by pass the transmission harness all together.

But the information in here about the transmission vent is interesting. and not something I have investigated.

But I will not spend 3-5k to replace a transmission harness / ECU on this car.

I'm not sure this will address the issue because I think it is in the connection at the computer where the fluid is causing your malfunction that sets off the trouble code. My understanding is the sensor is 'downstream' and not physically contaminated by the transmission fluid.

Ok so I'm pretty sure I found the transmission breather. In the pics I'm pretty sure it's the rubber hose (left side of pics) with squeeze clamps and what looks like a plug in the end. I got the pics by sticking my phone behind the motor from the engine bay. Can't really access it from below. Still not sure how to access it from up top either.

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hmm, if thats the case, it sounds like a routine maintence of cleanign the ECU plugs might be the best bet (considering it only takes about 15 minutes to do.

maybe a thin sponge or paper towel in the plug at the ECU to "soak" up the fluid.?