Hi, new owner of a GL320 CDI here, with the seven speed- I believe - 722.9 transmission. I have noticed two or three times over the past month that it got stuck in limp mode, not allowing any other gear than second. Scanned and found two faults:

• Y3/8N1
  • 0717 - The signal from component Y3/8N1 (Turbine Speed Sensor (VGS)) is not available
  • 0718 - The signal from component Y3/8N1 (Turbine Speed Sensor (VGS)) is defective

Some research shows me that most say the conductor plate above the valve body needs to be replaced because it is said the sensor cannot be replaced. A new conductor plate is expensive and would need to be paired with the ECM. A lot of unnecessary trouble it seems though, because the speed sensors are just soldered in. I see sensors available on eBay and amazon and it looks pretty simple to replace both speed sensors. My question here is, I can't seem to find any procedure for replacing, and torque values and pattern for the valve body. I've searched, but just haven't found it get. So, anyone have any experience with this? Any docs or howtos that can be shared?
Thanks and merry Christmas!

This is a common and fairly simple procedure. Search vendors on eBay and check feedback. You will need to ship your tcu and they will return it in a week or two. About $300 or so. Good luck

Hi alx, thanks for the reply. I did see this service offered on eBay and other sites, and many seem reputable. But I got to thinking, maybe I could take it a step further and swap the sensors myself, if that's all that needs done. I figured I could just as easily solder connections. If more is involved like adaptation, which I don't believe to be true, I could still go with this service. 300 dollars or so is much easier to swallow than a $3000 visit to a technician, but $35 for two sensors and a tool is even better. I just like to do as much work as I can myself. Saves dough, and helps me learn more about the vehicles I own. I thought I would call one of these service places today to see if that's all they do, who knows they might be happy to share some how to info with me. I was just surprised, all the videos I see of the sensor swap are in Chinese or Russian. Can't find a good video or procedure in English.

You probably saw this video , and it looks like the sensor might be indeed integrated. Yes, try to fix it yourself, soldering is not hard. BTW, what tool did you use to scan for the codes? I am looking to buy a scan tool for mine but can't afford a Star scanner. thx

It is a bit more involving than just unsoldering and soldering the new sensor. No need for adaptation.

Johny75, I simply used my 'el cheapo five-dollar bluetooth obd2 diagnostic dongle with the obdcardoctor app on my phone. I can clear the codes with the ECM powered and the engine off. I might plan on getting the icarsoft MB2 diagnostic scanner. They're around $150 to $200 on amazon/ebay/etc. It seems like it can do a lot, just not module programming, which wouldn't help here if I decided to get a new TCM or wanted to "virginize" one and then reprogram. So that said, I might still seek out some version of the STAR diagnostic system or similar.

Yea, I did see that video you posted. This one and many others like it seem to note the "proper" way to rectify the sensor by purchasing a new conductor plate (and often said the valve body too). But yea, if it's the sensor alone that's the problem I figure I could just replace that sensor alone. I saw a couple of other videos that show the use of a special punch tool to cut the plastic around the top of the speed sensor(s) that is holding them in their respective sockets. The person first de-solders the three connections on the speed sensor and folds up/back the piece of ribbon cable, punches (cuts) the plastic holding in the sensor, pulls the sensor out with pliers, and then places the new sensor in the socket, melts the plastic a bit around the top of the sensor to weld it in place, and then re-solders the new sensor pins to the ribbon cable. Looks easy-peasy. I do this sort of stuff every now and then at work.

These videos I find show the work being performed but do not include any tips or tricks or say that anything must be done after the sensors are replaced. Here's two videos (in Mandarin/Chinese) that show this procedure. The first shows the soldering involved and the plastic welding of the sensor into the conductor plate plastic body once replaced. The second shows the use of the handy punch tool that cuts the old sensor from the plastic body.

It appears that this is the only work involved.
Alx, anything else I'm missing? You say it's more involved than just de-soldering and re-soldering. Is the additional work you're referring to -the removal of the sensor via the cutting punch? Something else? Have you performed this sensor swap yourself in the past? I'm thinking this looks like all the work that should be performed, and simply reassemble everything and perform a trans fluid flush including the torque converter. -And of course, a new trans filter and pan gasket.

I figure since most sensor sets I am finding on ebay/amazon come with both sensors and a punch, I'd just replace both sensors while I'm there. I'm guessing if one sensor is acting up the other won't be far behind. I am confused a little on the parts though. A lot of them I find on ebay are for 4 or 5 sets. Only one set is needed per transmission, so it seems like these are usually bought as a lot by service shops willing to service the 722.9 transmission conductor plates.

Here's a link to one set of y3/8n1 and y3/8n2 sensors with a punch tool on ebay. If the link is down after this is posted a quick google search will find this part.
I guess my only concern with this is, it seems like all these sensors are made in China, sold from Shenzhen or HongKong. My experience with most Chinese parts makes me lean away from this, but I'm guessing Chinese sellers are the only ones that can get away with this because of the lack of or loose patent laws. But maybe this is a quality part, no telling I guess. But there might not be any other option.

I found a site that gives more detail on what's going on and a very general procedure on valve bocy and conductor plate procedure here.
This site mentions that I would have to know whether the conductor plate is a VGS 1, VGS 2, or VGS 3 model, but I don't think this would matter if I'm replacing the sensors. I hope someone could chime in to confirm. It seems like the site only covers replacement of the conductor plate, and they mention that the VGS 1 model would also require a new valve body, if replaced. No reasons are given, and I'm not thinking this would be necessary even if I had a VGS 1 model of conductor plate.
A conductor plate refurbisher I found doesn't mention VGS versions on their page. They simply show that they can repair the 722.9 conductor plate speed sensors. So I'm thinking the VGS version is a non-issue.

If I take this plunge and decide to do this myself I will be creating a detailed procedure complete with pictures and video.
Overall, this seems not a terrible thing to deal with, but it is yet another proverbial "iron in the fire".

yep, I later saw those other videos too. I would go for it, I myself do a lot of stuff myself and this does not seem too complicated, as long as you can afford not having your car operational for few days along with the the ability to lift it, etc.. : )

Right there with ya, man. I usually do it myself, or it doesn't get done. Trust issues I guess
I guess I'll be taking the plunge. Hopefully I can wait till it gets a little warmer. It was 0F earlier this week!
-Wish me luck!

Allright. So the turbine speed sensor issue is getting more prevalent. We're now getting stuck in limp mode at least once per trip. It's time to pull the trigger and fix this. I usually see the turbine inlet speed sensor as the faulty sensor, but maybe every one out of 20 times I'll see the outlet speed sensor show a fault too. (Yes, this transmission has gone into limp mode on us over 40 or so times since this past winter!) The TCU does seem to indicate issues with the speed sensors more when accelerating harder during trips. I've noticed it happens more often on our trips where it's the "we're late, gotta get there 2 minutes ago" type of trip, rather than the leisure "let's head to moms after church and we'll get there when we get there" type of trip. I do think that quick changes in speed causes the speed sensor(s) to produce a less than optimum signal. Since it's still summer and I'm wrapping up some other car projects.. (well, I guess this just means they're getting put on hold...), I'm going ahead with it. I will be replacing the sensors on the conductor plate myself, and not taking the car in to be serviced, nor sending the conductor plate in to be serviced itself. This is, of course, unless I see a large amount of metal and/or clutch material scattered around the valve body and in the filter. If it's that bad I'll need to rebuild the transmission and replace clutches and/or valves, and if that's the case I'll just have to take it to a local service shop to have the work done, as that'll be a tipping point between cost in terms of money and cost in terms of time. I won't be able to rebuild a transmission myself in under a month or two I'm sure with the fact that I only have 1-2 hrs each morning to work on things and that this would be my first transmission rebuild. It would be a good learning experience, but I'm not about to take time and learn on the family hauler. Cramming all four of us in a Jetta with two rear-facing car seats is a no-go!

I've ordered a few parts, and I'll get started on it shortly after they arrive. We'll have to deal with the Jetta situation for the week-ish it's down. (or a Saturday, if everything goes smooth!)
I ordered the Mercedes 722.9 Transmission Service Kit (722.9) - OEM 7229ERLYSK1 Kit from FCPEuro for $82.99, and the Y3/8n1 and Y3/8n2 sensors with a handy punch tool from ebay for $40.98.

Here is a valve body replacement procedure I'll use to help guide me:
And here's a document that I'll also use to help guide me with the removal and reinstallation:
http://weistec.com/media/productfile.../2/7229_vb.pdf

I also found a slightly better video of the sensor removal procedure from the conductor plate. It is still in chinese, but there are at least subtitles in english to help solidify my assumptions just watching the video:

I will be taking extensive pictures and a video along the way to give better instruction and detail for the next poor sap out there who wants to tackle this themselves.
I'll either report back in this thread or create another how-to thread with a better, more searchable title.

-Wish me luck!

Any word on your progress brah??? I am next in line for this exact procedure. The stealer will not get $2500 from me!

O, wow. I totally thought I posted details of my experience. Last year has been a busy one. Yes I fixed the speed sensor and the transmission has been rock solid since I did the work in October of last year (so, 6+ months?). I found all the photos I took and the service bulletins I used. I'll create a thread in the next day or two and post a link to it here. Essentially, I removed the valve body, and sent the conductor plate to circuitboardmechanics and let them do the work. It was a bit more expensive than doing it myself ($40-ish for the sensor and (really crappy and untrustworthy and totally useless) punch-removal tool, but ~$300 for them to do the service wasn't really bad either. They've done the job several times before, and I'm sure I would've ruined the conductor plate if I kept trying to extract the sensor from it. Then I'd really have a problem on my hands, as Mercedes will only sell the conductor plate with a new valve body (from what I remember), and I think they'll require a certified MB mechanic with STAR to connect to their network to pair the TCU with the ECM. Such stupidity and totally DIY unfriendly. But going the route I went I had no issues whatsoever. I sent my conductor plate in, they fixed it and had it shipped back to me within a week, I plopped it back in with a new filter and new fluid and has been flawless since. I'm no longer afraid to give it the goose when entering the highway for fear it would put itself into limp mode. I've also pulled my trailer several times, a few with ~5k lbs and it has pulled strong. I also have noticed it is behaving better when coming to a full stop. It used to clunk into 1st too soon when coming to a stop, mostly when the trans was cold. Now I don't have that issue. I'm not sure if the speed sensor or the fluid changed helped that issue.. but I'm glad that's taken care of too.
I'll find some time to post my experience with the speed sensor fix here in the next day or two.

I finally finished a writeup on my experience with fixing the speed sensors. I wrote a how-to/what-I-did HERE.