My transmission keeps going into limp mode. Sometimes the gear and mode (S/C) show on either side of the mileage and sometimes they don't, It's pretty random. Sometimes it just work almost right, but always shifts hard from first to second.

When the problem started I looked on the interwebs and found a possible solution, which was to get a kit to replace the plug receptacle. It came with the filter and gasket, and I had to change the fluid in the process. That seemed to work, for about a half hour, then things went bad again.

I checked the TCU, no fluid had crept up into it, so I dismissed that as the problem. I checked the brake switch and it appears to be operating properly.

So I went back to the interwebs, and replacing the conductor plate. It was cheaper to get the kit that had everything I already did, so I went ahead and got that. When I pulled the valve body out, the conductor plate was a mess, so I was sure this was going to work. No. Worse than ever. Limp mode all of the time.

Now I don't know what to do. Maybe it's not even the transmission. It's driving me nuts and it's about to be my daily driver again, so I can't afford to have this crap happening.

Does anyone have any ideas?

Thanks

EDIT: OK, this is kind of dumb, but I didn't have a check engine light, so I didn't check the codes. Turns out I have a P0705. Weird that it doesn't cause the check engine light to come on. Anyway, I'll look around the forum for the solution, unless someone can just point me in the right direction.

EDIT: The info I'm finding is that it might be the shift module, though it sounds like I need to get a more advanced computer connected to it to see what the TCU codes are.

I've looked into the Star clone, but it was always more than I wanted to spend. Those other two options look reasonably inexpensive though. Thanks.

For all the time and money you've wasted throwing parts at it, you could have already paid for a professional diagnosis, and probably the proper repair. Stop "saving money" and let a professional handle it.

@MBWagonNut Do you still have the three M-Bs listed in your profile? A Star/DAS/Xentry system is what you have needed for quite some time.

As of tomorrow I'll just have the wagon left.

Wow, yeah, thanks for the fantastic advice. Good for you feeling comfortable jumping right in with some smug judgments based on stupid assumptions about how much money I've spent and what my intent is. Super helpful. A+

You're welcome.

I've been working on my own cars for 35 years, and I don't do it to save money. I do it because I like to. I do it because every time I take on something myself that I've never done I increase my knowledge. I do it because I have teenagers who work with me so they can learn to have the courage and self-reliance to tackle new things. I do it because I'm an engineer and that's what engineers do. I'm not too cheap to pay for someone else to do it for me, I'm just too interested in doing things myself. I can afford to, and do, take my cars to the shop when I don't have the time (or patience, or specific tools) to fix them myself. I can even afford to really screw up and then pay someone else to fix my mistake. Anyway, as I said, you've made a bunch of assumptions and judgments but provided no real help, so why are you on my thread?

Also, trying to equate a person operating on himself to working on his own car is just ridiculous. Did you even think about how bad that comparison is before saying it? Take my advice seriously and stop saying that, it doesn't sound wise.

You're an engineer huh, so there's the first problem. I've met many engineers who owned a Mercedes, and not one of them could grasp what needed to be done to fix it. Typically they over-analyze the fault. Everything you've said and done so far tells me you're in over your head on this one. It's not a Honda or an old Chevy with a carburetor, it's an over-complicated feat of often backwards German engineering, so, my comparison with an operation stands. You can put a band-aid on a cut without much knowledge, but you wouldn't want to sew yourself up! Anyhow, good luck!

@MBWagonNut You are working on a computer and software controlled mechanical device. I am confident you know this. You need a proper computer and software diagnostic tool. To wit: Star/DAS/Xentry.

I've looked into this several times and couldn't decide which way to go. I almost bought one earlier this year. Do you have any specific recommendations?

@MBWagonNut Message @pmercury on this site, he can help.

Problem Solved. In case anyone comes here looking for answers, here is how I solved it.

I did a full scan came up with a P240C code "The selector lever position sent from " blah blah blah " is implausible and a P1856 code "Selector Lever Position Detection Has Failed." Searching these forums and others suggested there was a problem with the shift module. I pulled out the shift module and dismantled it, looked it over, cleaned it, and reassembled it. I found that the push button start wire had been sheared off somehow, but otherwise things looked ok. I reinstalled it and, though it worked better than it had, it still failed. So I started looking around for a replacement. The direct replacement 211 267 29 24 had been superseded by 211 267 63 24. Both of these part numbers were either hard to find or very expensive, probably because the push-button start was rarer. I looked in an online MB parts catalog and found that the new part also superseded 211 267 49 24, which is the shift module for the 2007-2009 models, and was able to find that part used on ebay for $99, so I offered $75 and it was accepted. I installed the part and did a bunch of testing and everything works.

All told I'm probably into this 8 hours and $300, however, the transmission service needed to be done anyway, so I really didn't lose much. I probably could've shaved off 2-3 hours and $80 by not doing the basic transmission service twice.

thx Chassis