Hello, I just joined the forum but am not new to MB ownership; I have owned several W124 and W126 sedans and a R107 many moons ago. I recently purchased a W163 ML430 and enjoy the truck but am still trying to adjust to its variety of electronic quirks.

My main concern is that, on occasion, for what seems to be no reason at all, the transmission will enter 'limp home' mode, i.e. it will not shift out of 2nd gear. This takes place completely at random. Most times when I crank up the vehicle it doesn't happen, but sometimes it does. I have done a little online research and as best I can tell the most common causes include a weak battery, a defective 13 pin connector pilot bearing, or a conductor plate failure.

On one occasion where this took place, the SES light came on, and according to my code scanner it was showing a P0700 code; however my tool is a basic Snap-On model and does not have the capabilities to give me any further information. When I purchased the truck it had an older battery in it, I replaced it with a new one, hoping that quick fix would solve the problem, however I did not see a change. Also, following the battery replacement the BAS/ESP light came on briefly, then went out.

I have ordered a dipstick tool to check on the fluid level, but I would like to know how best to diagnose further in order to determine whether I need to replace the connector, the conductor plate, or something altogether different. Any and all replies are welcomed.

Welcome to the forum!

Any P07xx is a transmission issue. It is a generic code when read from the OBDII port. Now, you are locked-in with the code, and the only way to reset it after the repair is through the circular connector in the engine bay. You will need the Mercedes Star, Carsoft, or the SnapOn Scanner with the adapter cable. The SnapOn Scanner needs to have the software cartridge for Mercedes and the appropriate personalty keys.

The big question, is the SUV firmly staying in 2nd gear, and how is reverse? It too is firmly in gear too? The gear is not going to neutral? This is very important! I work on these transmissions, and the gear will not stay in 2nd or reverse in limp mode the problem goes to the forth dimension with compounding issues...

You have done well by ordering the testing dipstick. The fluid is the number one thing as it could to high, low, or old? I suggest the fluid be no more than few years old. How does the fluid look like-redish of some sort?

Your problem may be the immediate three of the very common problems:

A) Ruptured/non working speed sensor on conductor plate-See picture in post 35 in the link below:

722.6 Transmission Refresh. DIY and questions.

If your snapon scanner has a scope feature, you can watch for the missing return pulse from the conductor plate of either speed sensor. Like in this article:

http://www.valvebodypros.com/pdf/Mercedes722.6_Failure_to_Upshift.pdf

You watch the pulse before you make the mistake of buying the part.

B) The circular electrical connector that controls the conductor plate will fail by losing the sealing properties of the o-rings which is a very common problem on all 722.6 transmissions. See the thread below..

C) If the Circular Electrical Connector breaks through more than likely the transmission fluid wicked it's self up the wiring harness, and into the transmission computer in the computer coffin, so also check the transmission computer for fluid wetness at the two connectors. I would even take out the computer out(it floats out once the connectors are removed). I would check it for fluid contamination by turning the computer upside down, and watching fluid come out...See post 5 on the link below:

My attempt at replacing the transmission plug. - Mercedes-Benz Forum

If you find the computer connectors to the transmission computer are wet, fluid came out. This is how I clean them(Post15-fluid in the TCM):

High Mileage Questions/Testimony please. - Mercedes-Benz Forum

If you want more data, on this wonderful transmission, and it the best to DIY for the first time. Here is the service manual and a deep troubleshooting manual by Mercedes..

http://www.all-trans.by/assets/site/files/722.6.pdf

Download the attachments in post 3 and 4

97 e420 722.6 in 2 gears at once!!.

This should get you rolling for now..

Martin

Thanks for your help Martin! It does stay firmly in 2nd gear and firmly in reverse, and that gear seems to function normally. I'm waiting until the dipstick comes in to do anything further with the truck, but I will update everyone then. Thanks again.

The info provided by MAVA is golden.
From your description above it sounds like the conductor plate.
I have seen this problem twice(one being my own), both had exactly the same description as you gave and both turned out to be the conductor plate. These transmissions are very good and I have only seen problems with the conductor plate, oil leaking out through the bell housing seal or circular connector and some claim there is a regulator spring that fails. If the oil leaked out it will go to limp mode very quickly after starting, not at random times.
The random occurrences have always pointed to the conductor plate.
It's expensive, but wont bankrupt you and as you have already invested in the proper diagnostic equipment follow the route of proper diagnostics first.

Another sign of a conductor plate at the end of its life is occasional harsh shifts regardless of RPM.
The conductor plate is a piece of plastic with copper tracks on it. On the one side it connects to the circular connector for the transmission harness, then it branches out and has these pads that press against the terminals of the solenoid valves that are fixed to the transmission. They usually corrode on these contact points with the valves or the seal around the circular connector leaks pushing oil up to the shifter(never seen this myself but have seen many posts).

Good luck and let us know what you find.

Update - My transmission dipstick came in yesterday, so I was finally able to check the fluid level. As I had seen others on the forum recommend, I made sure the transmission was up to the correct operating temp before checking. It showed on the dipstick to be in the area between the 20 c and 80 c zones so I am assuming that since the vehicle had been running for about 20 minutes (and driven 10 miles before I did the check) that it is a little low on fluid?

Yes, between the 20 and 80 would be low. You want to be between the 2 marks on either side of the 80. Add fluid slowly. It won't take much.

I just did this to my 2000 C280. It would go into limp mode after a few stops typically after just getting off the freeway. When stopped, moving the shifter resulted in really harsh shifts. Restarting the car would reset it. This worked a few times until it was stuck in 2nd for good.

If you don't know the service history of the car, go ahead and do the connector along with a filter and gasket and some new fluid. You might get lucky and this is all it is. If not, then you've wasted the fluid and next is a new conductor plate.

Use MBZ connector only, only about $12 on ebay. You can get the plate there too for about $130. My old plate showed no obvious fault.

Wolfpack, did topping up fix your problem? I just had a small amount of "sealed" fluid loss. I just got my dipstick but am not sure I want to top off with the Mercedes fluid which is now made thinner for the 7speed transmissions. I keep reading we can use Mopar and Valvoline as substitutes for the "no longer" made ATF from MB, what did you use?

__________________
Ed "Don't Benz's just feel better..."

Current wives...
2000 ML430 Skyview "The Mel"
2000 CLK430 Cab "The Cab"
85 300D Turbo "The Diesel"

Past wives...
92 300E
85 190E

"One should as a rule respect public opinion in so far as is necessary to
avoid starvation and to keep out of prison, but anything that goes beyond
this is voluntary submission to an unnecessary tyranny, and is likely to
interfere with happiness in all kinds of ways."
Bertrand Russell

I know this is an older thread, but I have a question.

My ML320 is stuck in limp mode, and I have replaced conductor plate, connector, etc and repaired lots of melted wiring etc. Now the truck is stuck in limp mode. I have an iCarsoft scanner, and its saying that the Lateral Acceleration sensor is faulty. When tested with a normal OBDII scanner it says "Solenoid C Electrical" fault.

When I try to clear TCM Codes, with the carsoft it says unsuccessful. The car remains in limp mode.

The question is, will my iCarsoft that works through the OBDII port allow me to reset the transmission and bring it out of limp mode, or do I have to have some kind of other computer that links to the car "under the hood" to do this??

All of my repair experience has been with pre-ESP cars, and I've never had this problem.

It's driving me crazy!

__________________
Current cars:
2000 ML55 AMG, 174k miles
2003 C240 T-Modell, 202k miles
1995 S320, 207k Miles

what year is your ML? I want to say after 2003 everything is done through the OBD port, but earlier in the engine bay is a 1-1/2" black circular connector that the limp mode is reset through.

Martin

Well, from what I've been reading, it seems as though the W163 models do NOT have a 38-pin diagnostic connector under the hood or... anywhere.

Apparently the Mercedes SDS only connects through the OBD-II port on the W163 model. Can anyone verify this??

__________________
Current cars:
2000 ML55 AMG, 174k miles
2003 C240 T-Modell, 202k miles
1995 S320, 207k Miles

Correct..........

Ok, I'm not sure if I should start a new thread, so I'll just ask here first.

My particular 2001 ML320 has a check light, BAS light, flashing Low Range light on startup and is stuck in limp mode.

I am getting codes:

C1142 - Lateral Acceleration Sensor, Open/Shorted

different module:
P2061-004
P2061-016
P2061-064

I have replaced the conductor plate, 13-pin connector, and renewed fluid and filter. I also repaired melted wiring going to the 13-pin connector.

None of this made any difference.

Clearing the codes doesn't make any difference. The lights stay off for about a minute, then come back on.

I'm at a loss with this one. I am assuming the Acceleration sensor is a separate issue and will not put the car in limp mode?

Could I be looking at a bad TCM? When I try to access the "Transmission" computer in my scanner it only says "Communication error".

__________________
Current cars:
2000 ML55 AMG, 174k miles
2003 C240 T-Modell, 202k miles
1995 S320, 207k Miles

can you remove the TCM and physically check it and its wiring.

__________________
2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)