weppler1978

Hi

I own a 1999 e320 sedan, 120,000 miles. Ran fine up until about 2 months ago when the gears would slip occasionally. Brought it in to a mercedes repair shop in town that specializes in foreign cars and they recommended changing the transmission fluid. Did that at a cost of $300. Helped at first but a couple weeks later it happened again. Then about 3 weeks ago first thing in the morning I when I took it out it wouldn't go past first gear. Drove it to a gas station, and left it running a few minutes. Turned it off and on again and then its fine. Ran fine the rest of the day. That has happened twice, once when backing up it revved high and had to let it sit for a while, and the other same with first. Both times it was fine again after several minutes and didnt occur the rest of the day, always happens first thing in the morning. Also it does slip more often, i.e. Ill be accelerating and it will change gears a little rough and go back down a gear then back up.

I had to replace the ignition module about a month ago at a mercedes dealer (yikes that was expensive) and asked them to take a look at it and they told me it was fine, couldn't see anything wrong with it.

Any ideas? I don't know if its electrical, or the transmission or what, but I am running out of ideas and getting worried about my poor car.

Thanks

Bill

Musikmann

IMO there is definitely something wrong. One easy thing you can do yourself is to look for AT fluid incursion to the transmission control module. That will cause a lot of strange symptoms.

When the dealer took a look did they check for transmission error codes using their scanner? Or did a tech just take it for a test drive and give you the old "could not duplicate" scenario since it didn't act up for him?

weppler1978

Thanks for the response. I believe he took it for a test drive, as they told me it "felt" good. How do I look for AT Fluid Incursion?

Musikmann

There is a box with a black cover containing the control unit on the passenger side of the engine bay. Take the cover off and inspect it. If you search you might find a thread with photos, I know I have seen one somewhere, but maybe not on this MB forum.

Musikmann

Just to add: I did a quick search for TCU and didn't readily see a good DIY with photos but there might be one somewhere. Also if you find fluid you have a leaking connector (also called a pilot bushing and other things) that allows ATF to wick up the wiring harness and into the TCU. This a pretty common problem area on these cars.

weppler1978

WHen I looked it up I see references to on under the shifter in the middle below the console. Is this what you're refering to or is it something else?

I looked under the hood though and saw two boxes on the passenger side, one I unscrewed but there was nothing under it. the other has a lot of electrical stuff in it, like lots of fuses and wires, says its connected to the battery under the rear seat.

Again I appreciate your help, I am at my wits end and the dealership is an hour away from me so I am hoping I can figure it out at home and also not have to spend thousands at a dealership unless I have exhausted all my options. Thanks

Musikmann

No that is a different issue entirely and involves a liquid spill into the shifter. That causes a limp mode unlike what you described. It would not drive normally again without drying that out and someone with a sophisticated scanner clearing the transmission error codes.

The box with a lot of electrical stuff sounds like where you ought to be looking for the ATF. But we have different model years so possibly yours is in a different location. But it should be under the hood somewhere.

Musikmann

I just found another search term (ETC) for electronic transmission control module so that might produce better results.

weppler1978

Okay, found a link with pics on how to remove it, its right where you said it was. Took the lid off, removed the wires and pulled it out, and it is dry as a bone. Put everything back together, back to square one with one thing ruled out ! Other thoughts?

Musikmann

Glad you found that link.

I'm trying to understand why improvements after the fluid change only lasted the 2 weeks. Do you know if they changed it all or only dropped the pan and replaced some of it? And do you know what type of ATF they used? I'm asking because some people have said the the newer 7-speed MB fluid does not work well as a replacement (or mixed with) the older 5-speed fluid. I'm also wondering if they knew how to measure the level. These transmissions are pretty finicky about that. Another thing, did they find any metal particles in the drain pan?

It might be time to have someone read the transmission error codes. The inexpensive OBD2 ones don't do a very good job since they can only read some pretty generic ones.

There are reports that AAMCO will do that for free and maybe the shop you took it to can (or already did) as well. If you can get codes it should help pinpoint the problem.

weppler1978

They flushed it, they said it looks like it had never been changed before and was pretty nasty, but made no mention of finding metal. I know they used the benz fluid as I asked when I went there if they used a certain one and they said for Mercedes they only recommended using one specific kind and to not use generic or off the shelf, and its what they use at the dealer.

Too be honest as to why it only lasted 2 weeks after they changed it, my gut is it never really made a difference, and it didn't help. My wife was the only one driving it at the time and I am wondering if she noticed it or not. It was when I drove it 2 weeks later I noticed it and asked her if it had been happening and she said not that she was aware, but she isn't the most attentive driver.

Is there anything else I can check you can think of before dragging it an hour to the dealer? I'm out like $2000 in the last 3 months on repairs and don't think I can take much more, lol.

Thanks

Bill

Musikmann

Thanks for answering my questions and that clarifies some things.

Transmission flushing under pressure is generally not recommended on a car with that many miles, and especially the first time. Typically they don't even drop the pan to look for metal shavings, wipe it out or change the filter.. They just hook the machine up to the transmission lines and force fresh fluid through there until it comes out clean. It has been said that this process can dislodge "gunk" that is better left where it lies.

My only other thought at this point is to find a shop that can pull diagnostic codes from the TCM to see what's there and you might be able to do that locally. Then post those here so some of the real gurus can have a look. I'm certainly not one of them, just trying to help.

Musikmann

This might be important. Do you know if the shop cleared the tranny error codes? Based on your symptoms there almost had to be some. They don't just go away after a few drive cycles like the ones that cause a check engine light. So, if the codes remain, so do the symptoms, even if they fixed the problem. Anyone with a scanner sophisticated to read them, can also clear them.

The only other do-it-yourself I can think of is to check the fluid level. It's not that complicated but it requires a special "dipstick tool" (member ohlord, dealer, ebay). You have to check it against 2 marks; one with the fluid at 25 C and the other at 80 C. As I said earlier, level is pretty important in these sensitive trannys.

Musikmann

With fluid that fresh I don't know how much that will tell you. My guess is it's still nice and red or pink, with little or no contaminants.

weppler1978

Okay, another question, it actually has been doing "okay", but yesterday driving after a day of no issues I got it into my head maybe it miraculously fixed itself, yes I know this was dumb. I had tried to recreate the jerkiness and slipping and nothing. So I floored it for 3 seconds. Let off gas, and it shifted down pretty hard, then when I pushed the gas it just revved, I was going about 45 mph at the time and lost all acceleration. got into a turn lane and came to a stop, and it started back up fine from there. Does this help with a diagnosis at all or not?

I'm guessing it is that plate you're talking about or the transmission unit thing under the transmission, just postponing taking it in right now for a week.

Musikmann

I'm a novice too so that doesn't tell me anything. The only plate I know of is called a conductor plate (inside the transmission itself) which has speed sensors on it. A lot of people have replaced theirs but I'm not clear on all the symptoms and diagnostic steps. And the only unit I know of is the TCU under the hood that you checked for fluid but found dry. There is also a gear selector switch inside the shifter apparatus but I have no idea if that is at fault.

I still think you need to have someone read the tranny diagnostic trouble codes with a scanner capable of doing that. Then hopefully someone with more knowledge will chime in with the fix.