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  #1  
Old 06-22-2005, 03:39 PM
1994C220's Avatar
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Join Date: Aug 2001
Location: Iowa City, Iowa
Posts: 124
Unhappy Trans Control Module (TCM)

Has anyone changed out a tranny control module? I would like to know the procedure. I have searched for days both here and on benzworld and although everyone mentions replacing it, no one actually says where it is exactly located, or if there is an exact procedure for it. I have an ongoing shifting problem on a 98 ML320. I have taken it to several independent shops and have gotten different reasons for the hard shifting problem. I had the dealer check the transmission fluid and it is "acceptable." I have changed out the trans fluid, have a new transfer case, changed out the MAF sensor, and still have the shifting problem. The thing with the shifting is that sometimes, the car shifts wonderfully....it is when you have to accelerate rapidily that the shifting gets screwy. Im wondering if the MAF sensor could still be to blame? I bought the sensor used, and just figured that I would change them out and if it got better it was the MAF sensor, and if not, it was something else...perhaps they are both bad?

Anyway, could someone please give me info on the transmission control module? Is it as easy to replace as the MAF sensor? I thought I saw a mention to it being under the drivers side steering wheel???

Thanks for your help,
Carlos
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1994 S320
131K miles

1998 ML 320
126K miles

1994 Blue C220
122K miles

Im going to Grad School @ the University of Iowa
Go Hawkeyes!!!
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  #2  
Old 06-27-2005, 03:09 PM
1994C220's Avatar
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Join Date: Aug 2001
Location: Iowa City, Iowa
Posts: 124
Update on TCM

I have a bit of an update. I just bought an Actron scanner off eBay and received it today. I hooked it up to my 1998 ML320 and it only gave me one code, P0400, which is the EGR valve or from what Ive read the tube. I will have to find a place where I can tinker with removing and cleaning the EGR valve and tube to see if I will need a new one or not.

My question is this...If the TCM is bad, would it show up on the scanner? The check engine light is not on, so I was surprised to see the EGR code in there. Thanks for any help.

I cant wait for my wife to get home with my 94 S320....Im sure it will have quite a few more codes because it has been running like crap lately. I hope I dont see EGR code on s class because my shop was supposed to have cleaned out the EGR tube, and I replaced the EGR valve with a new one just for s*&U('s and grins.

C
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1994 S320
131K miles

1998 ML 320
126K miles

1994 Blue C220
122K miles

Im going to Grad School @ the University of Iowa
Go Hawkeyes!!!
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  #3  
Old 06-27-2005, 03:16 PM
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Join Date: Mar 2003
Location: Manhattan, NY
Posts: 54
tranny problems

What do you mean that the shifting is screwy?

Do you mean it slams into 1st and 2nd after holding the gear too long or will not shift at all or what.

I think the Transmission control unit is under the shifter but don't quote me. If I'm thinking of the right part, it's the one that gets screwed up when someone spills the big gulp on the shifter.

I had the hard downshift problem which was mostly fixed for years but comes back once in awhile. I know how to work around it so it is very seldom. IN my case that involved changing a bunch of plastic valves in the tranny 2 times under warranty thank god.

Last edited by bigcatny; 06-27-2005 at 03:26 PM.
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  #4  
Old 06-27-2005, 03:33 PM
1994C220's Avatar
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Join Date: Aug 2001
Location: Iowa City, Iowa
Posts: 124
Thanks for reply

Thanks for your reply. Our ML has had this problem since we have owned it almost, so it sounds like we might have the same problem. Since this is wife's car, she rarely notices it anymore because she drives it cautiously to avoid the lurches and clunks.

If you really floor it from a stop, it will give you whiplash when it shifts into higher gear. it doesnt really delay or give high rpms, it just kind of pops into the gear suddenly and it makes your head go back from the thrust.

The main time you feel this problem is when you are decelerating(say coming to red light, and the car is downshifting) and then the light turns green....if you push the gas down too hard, it will jerk itself into the low gear and you get a nasty touch of whiplash(well, its not that bad). So in order to keep it from doing that, you just have to apply gas very slowly.

I know by now that it is not the transmission(at least internal) because after 3 years, I shouldnt have anything left of a transmission. I have tried in vain to correct it...dealers are clueless, indies too, and I have changed fluids, run diagnostics, replaced the transfer case(this helped a little), but the problem remains. I have begged my service advisor in Austin to ride with me since he claims he cant duplicate it on several test drives(Bull$##$), because I can make it do it 100% of the time. He is really pompous and Im glad Im up here in iowa now. Im sorry I dont have an 80K mercedes, cause if I did Id have him kissing my butt! Wait till i get out of grad school. I may go by there just to have him suck up to me.
Havent tried the Iowa City dealer yet, maybe I should see if SOMEONE will let me show them what I mean.

We love our ML, but the trans thing really annoys me. For now, my wife is happy with it other than the fact that the AC doesnt work because of a relay short somewhere under fuse box. We are hoping to fix that this week. Its hot here in Iowa today (95).

Sorry, got off topic. To get back to the trans....I have noticed that the shifter makes a clunking noise when you move from P-D or back, if anyone knows where the TCM is, or if it will reveal itself in diagnostic scanner, please please let me know.

By the way, this scanner is great. I know it will work with my 94 S320 because I have had my car scanned at autozone...its the same one they use...got it on eBay for 80 bucks.

C
__________________
1994 S320
131K miles

1998 ML 320
126K miles

1994 Blue C220
122K miles

Im going to Grad School @ the University of Iowa
Go Hawkeyes!!!
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  #5  
Old 06-27-2005, 07:39 PM
MB WRENCH.
 
Join Date: May 2005
Location: OREGON
Posts: 137
the ETC module (transmission) is under the drivers lower dash panel. It's mounted vertically.
- You should not mess with that trans. unless you know what you're doing.
And I am pretty sure you can not just plug a new module in - you need to transfer verison coding. I don't recommend trying DIY repairs on that trans. unless you have very good instructions from a trusted source.
A faulty shift recognition switch in the actual shift lever assembly will also cause erratic shifting problems -just like bigcatny stated.
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  #6  
Old 06-28-2005, 03:12 PM
1994C220's Avatar
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Join Date: Aug 2001
Location: Iowa City, Iowa
Posts: 124
So does a bad TCM or shift recognition switch show up on diagnostic?

Thanks for the info....I will not mess with the TCM i guess. the ML is in the shop because of the AC short, and interestingly enuff, he said he took the fusebox apart and it appeared to look good to him, when he put it back together, the AC started working again. He thinks it could be because one of the relays could have been seated wrong...

Another question. The shift recognition switch under the shifter....can it be replaced without any need for reprogramming modules, updates, chants in german, etc????
__________________
1994 S320
131K miles

1998 ML 320
126K miles

1994 Blue C220
122K miles

Im going to Grad School @ the University of Iowa
Go Hawkeyes!!!
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  #7  
Old 07-06-2005, 04:39 PM
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Join Date: Aug 2004
Location: KC, MO
Posts: 140
Should be able to switch out the gear recognition assembly without so much as a code; as far as the shifting problems, they have had several updates on that transmission, and you have valve body, VB electronics (conductor plate), and control module (TCM) that can affect your shift, plus the various electronic inputs going to the TCM, and the mechanicals itself. Start with pulling the codes, and if nothing significant comes up, have the TCM adapted (shift values erased and reprogrammed), and definitely have your fluid quality checked (I.E. regardless of what you hear, make sure the fluid is changed every 50-60K miles, ESPECIALLY on your older style tranny; they have 6 major updates on the tranny mechanicals alone on that since yours was built, and it's just a ticking time bomb IMO).

You cannot switch out the TCM without version-coding it first, but if you are buying it new or rebuilt, the supplier will automatically version-code it for you; they will need your VIN# to do it. There is an updated TCM, 0265450832 or something like that, so whatever module you buy, make sure it starts with "026", as I believe all the updated modules do. And yes, as long as you buy from a dealer and know how to adapt the vehicle (adaptation is a driving procedure to set the base settings on the transmission; it has to be done a certain way, but if you mess it up it will still drive, and eventually reset itself close to where it needs to be), you can replace it yourself. The new or rebuilt transmission control unit comes with no adaptation values, so when you put it in you will need to know the procedures to set the adaptation values (I'm sure they're somewhere on this forum).

I will hopefully be setting up a reseller account (as opposed to a wholesale account) for transmissions with a dealer, so the minimal discount I get for purchase of transmission can be doubled, and I can reflect the savings on to people such as yourselves. I think, however, if the members of this forum and other forums complained enough, the transmission would be made available at a greatly discounted price to begin with, as much of the problems are directly associated with dewign flaws inherent with rapidly designed major automobile componants. The reason it won't happen is the vast experience and knowledge it requires to even understand how these transmissions work and what specifically it is that goes bad on them is not within the realm of the common driver. But ask any of the major aftermarket Mercedes transmission rebuilders, and they will tell you the transmission has received major updates because of inherent weaknesses within the transmission; I would think that if MB could be made to extend the M111, 112, &113 warranties because of faulty lubrication schedules (even though it was related to using dino instead of synthetic fluid in many cases), some headway should be able to be made with the non-existant service intervals with the 722.6 series transmission, because the fluid breakdown and resulting friction in the center of the transmission is a primary reason of catastrophic failure of the center planetaries (primary cause of transmission failure), namely the center planetary support.
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Old 07-06-2005, 04:39 PM
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