TCM Transmission Control Module Fluid Contamination Cleaning and Fix

[220629]

First. Thanks goes to Cheyenne for a relatively simple fix to avoid TCM connector transmission fluid contamination.

Background.

Transmission fluid can migrate up to the TCM that is mounted under the seat. The fluid conducts electricity well enough that the free liquid can interfere with the low voltage/low current signals needed for the transmission module to operate properly.

How does fluid from the transmission get uphill to under the seat? The Transmission Connector Body for the electrical signals to/from the transmission is designed to keep transmission fluid inside the transmission. If the connector body seals fail fluid can drip out of the transmission, but it can also get in contact with the conductors aka wires. The insulated stranded conductors act like a tube. The fluid wicks up inside the insulated tube by capillary or other action to come out and accumulate on the TCM connector and even circuit board components. If enough fluid collects it can short the signals for the TCM. It affects sensor signals. It will not blow fuses.

It is important to replace the Connector Body periodically to avoid transmission fluid external drips/leaks and fluid migration to the TCM. Symptoms can include odd transmission behavior and heavy shifting.

Cheyenne suggests a simple way to break the path of fluid migration to the TCM.

... I still can't figure out how the oil got on the wires and on the connectors to the TCU being mounted under a seat ..

A type of capillary action or creep.

If you wash down the removed TCM using carburetor cleaner or alcohol it will likely return the TCM to proper operation.

vic

A question to anyone who can answer...

Why has no-one developed a simple male to female link harness to go between either the transmission and harness or harness and TCM to act as a 'drip leg' and prevent capillary creep into the TCM.

You could even cut the harness at a suitable point and insert any male/female connector to act as a break.

Surely a lot cheaper than failing TCM's?

Keith.

Good question and solution.

For DIY, a handful of insulated slide-on connectors would do the job. 3/16" or 1/4", even smaller will work. You only need to match wire colors one time for the slide-ons. Do one wire at a time. Do not cover with heat shrink. After slide connector install the OEM connector can be used as usual.

The fluid should drip off the open connectors.



The above said, TCM fluid contamination can be a problem, but it still seems more an "if" not a "when" for it to surface. I stuck a piece of facial tissue around the connector on my 2004. My theory is that the tissue will wick the fluid away from the contacts. Soaked tissue should conduct electricity less than liquid transmission fluid will. I haven't had any reason to be under the seat, so I don't know the condition of the tissue.

vic

 

[220629]

Another member here suggested that touching the wires with a hot soldering iron would “break” the capillary path and stop it from wicking past. I haven’t tried it yet, because I wasn’t able to understand how that would work.

My explanation would be that small spaces between the wire strands more readily move the fluid along. Soldering the wire reduces those spaces so only the outside surface is available for the fluid to creep along. That and the insulation aka "tube" gets interrupted when stripped off to allow access for applying the solder.

vic

 

[hkpierce]

I am in the midst of chasing a rabbit down a hole, and found that after about 40,000 after the last TCM R&R, I have wicking transmission oil into the ECU. I was actually looking for a problem related to Fuse Block 1/ Fuse 17, but noticed oil on my OM612 #4 ECU connector.



Here is what the ECU side looks like.


Upon closer examination I found some oil on the far wall of #5 also:


I used electrical cleaner on both the connectors and the ECU to rinse away the oil.

On the TCM side, I did not have a replacement, so I also rinsed it with electrical cleaner. I waited for about an hour before reassembling.


I have not had any significant issues that (as of this moment) I can attribute to the wicked oil. I am hoping it has nothing to do with the #17 problem; and just one of those things you run across when working on something. But there are reports of ECU damage. I am not ready to say that yet on mine.