722.6 Erratic Shifting Problems Solved
 

My 1998 E320 currently has 155K miles. Last year I had the car in the dealership to have new spring perches installed. While the car was in the shop (first time since I owned the car at 58K miles) they told me that the trans seal was leaking. I authorized the work since I was aware of this problem. When I picked up the car the invoice stated that they added transfluid. When I go home I checked the trans fluid level and it was low so I brought it back to the proper level.

Prior to this the car would have it's moments when shifting. When I punched it it would slam into gear. When I would accelerate moderate to heavy and maintain the gas peddle the car would go into neutral for a second as it was shifting from 3rd to 4th gear. When I didn't come to a complete stop and started to accelerate the car would jerk forward. Other then the above erratic problems the car shifted fine.

After researching this problem on the MercedesShop forum I read posts that suggested that the trans connector could have taken in some oil. I assumed that this was the connector at the transmission end but another thread pointed to the connector at the TCM. I figured that it was highly unlikely that the trans fluid would work it's way from the transmission to the TCM.

After removing the connector yesterday I was proven wrong. Below is a few pictures showing the trans fluid on the connectors:

http://www.peachparts.com/shopforum/attachments/tech-help/59610d1222816207-722-6-erratic-shifting-problems-solved-img_0008.jpg
http://www.peachparts.com/shopforum/attachments/tech-help/59611d1222816279-722-6-erratic-shifting-problems-solved-img_0009.jpg

As I started cleaning the connectors I noticed that trans fluid was leaking out of the TCM as I inverted it. So I popped the circuit board out of the plastic housing and here is what I found:

http://www.peachparts.com/shopforum/attachments/tech-help/59612d1222816451-722-6-erratic-shifting-problems-solved-img_0010.jpg

So much for "sealed for life". There must have been over 2 tablespoons of trans fluid in there.

After cleaning up the circuit board and connectors the board looks like new again:

http://www.peachparts.com/shopforum/attachments/tech-help/59613d1222816579-722-6-erratic-shifting-problems-solved-img_0011.jpg

I ended up cleaning up the board and connectors with brake disk cleaner. It is non-flammable, safe on plastic, cuts through oil and evaporates quickly.

After driving my car to work today, the transmission shifts normally again thanks to all you contributed to the various posts about the trans fluid on the TCM connector.

Excellent post thank you.

Very nice post!
Where is the TCM connector located ?
I m doing the transmission service myself this weekend and i d like to check for atf leaks in there.
Thank you

Yes, please post that info. I too am going to do mine in the next month or two...

Tranny fluid doesn't just magically appear in the TCM - it's getting in from a leaking seal or o-ring on the transmission. That part needs to be fixed to stop the problem on a permanent basis.

Otherwise - great post - nice to have pictures so folks can see and not have to envision what the OP is talking about.

Are you saying that the trans fluid in the TCM effects its operation? I wouldn't think the electronics would know the difference.

The TCM is located under the hood passenger side up towards the fire wall under the plastic box. It is the circuit board next to the relays. The board has two connectors, the connector towards the center of the car is the one that wicks the trans fluid, however you will need to remove both connectors to remove the TCM board.

wbrian63,
You are correct that you need to stop the leak. I mentioned in my post that I had my trans seal replaced last year but the dealer didn't know to check the TCM for trans fluid.

mpolli,
Most electronic circuit boards are not designed to operate with any type of liquid on them. With the trans fluid inside the connector to the TCM could have acted like an insulator. If there was any graphite in the trans fluid then any it could have acted like a short between the contacts on the circuit board. Best to keep electronics clean and dry.

You are absolutely right! the 722.6 has a known 'O-Ring' problem that may exhibit itself early on. Say 25K miles. Please read about my situation, with diagrams and p/n's for the fix at 722.6xx transmission leak

Here is a photo of the TCM connector in relation to the other components in the compartment:
http://www.peachparts.com/shopforum/attachments/tech-help/59640d1222912496-722-6-erratic-shifting-problems-solved-img_0013.jpg

It's the one with the blue shop rag wrapped around the wires.