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Discussion Starter #1
43k miles on my 00 ML320.

Started up fine, drove it 10 feet and nearly every warning light comes on, ABS, BAS, ETS, Do-Re-Mi. Then it does not shift out of first. After shutting down several times and restarting, the only light that stayed on was the CEL. Was able to drive home pretty normally with only the CEL on. In fact it drove just great.

Took it to get it scanned at Autozone. Code scanner came up with ERROR on several tries. Could not read anything off the terminal.

Still happens when I start it, and I have to go through the same ritual to be able to get out of first gear. I read a thread on the forum about trannys getting stuck in 1st and getting a huge shudder when engaging "D". Same here - except I am able to get out of that with my ritual.

Is my ECU fried?
 

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2002 honda civic (sold), 2009 Mercedes ML350
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normally when the trans goes into limp mode and your CEL is on, usually there is faults in the ETC. and they usually have to do with either the speed sensors or starter lockout, etc... My guess is you may need a new valve body or trans control unit.
 

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Anyone know how to test the valve body or tcu. I can get it out of limp home by restarting it. It drives fine when it does. Trans shifts smoothly and all. As for the ECU, I disconnected my battery to try to reset the ECU before I hooked up the code reader...the ECU was probably cleared of data and had to log new data before it could be read?
 

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you need to find out what codes are coming up if your CEL is coming on. where are you located?
 

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Discussion Starter #5
Streetglower said:
you need to find out what codes are coming up if your CEL is coming on. where are you located?
Houston, TX. Just got back from Autozone, the ECU reads now after driving for 15 miles after reconnecting the battery.

P0720 and P0500. One was VSS and the other was speed sensor output I think. Anyone have a link to a thread with all the codes listed? Can't find it on a search.

BTW - seems to go into limp home when <80 C engine temp. When I get her warmed up >80 C, has not gone into limp home.
 

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the speed sensor is part of the conductor plate. you wont need a valve body, just the conductor plate which sits on top of the valve body. you have to remove the valve body and then remove the conductor plate. the plate is around $300. the plate contains the 2 speed sensors and the starter lockout. very easy to replace. this is the reason why the trans is going into limp mode. I have seen it so many times. very common on the .6 tranny. now there is a chance its the trans control unit, but its a 50/50 shot. I have only replaced trans control units due to fluid contamination. check and see if any fluid is in the unit, if not, I would more suspect the conductor plate.
 

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Discussion Starter #7
Streetglower said:
the speed sensor is part of the conductor plate. you wont need a valve body, just the conductor plate which sits on top of the valve body. you have to remove the valve body and then remove the conductor plate. the plate is around $300. the plate contains the 2 speed sensors and the starter lockout. very easy to replace. this is the reason why the trans is going into limp mode. I have seen it so many times. very common on the .6 tranny. now there is a chance its the trans control unit, but its a 50/50 shot. I have only replaced trans control units due to fluid contamination. check and see if any fluid is in the unit, if not, I would more suspect the conductor plate.
Thanks for the good info Streetglower. If it is the speed sensor, could it be intermittently sending good/bad data? I can get it out of limp home and it drives great. Also - can it be tested? There is a chance it is an electrical connection/ground problem?
 

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usually once the problem starts, the car goes into limp mode untill shut off and restarted. then once the issue hits again, same thing, cars goes into limp mode. I have had lots of cars come in with these issues and i have replaced the valve body to correct the issue. some techs replace just the plate, but i do the whole valve body if under warranty. kill 2 birds with one stone.

now the conductor plate has electrical grids as I call it on it that all lead to the connection where the electrical connecter plugs into, then leads to the control unit. there is testing that can be done, would have to look at a diagram, but have yet to see a wiring issue with the harness, its a straight shot from the control unit to the tranny, the harness isnt but several feet long. but its either a control unit or electrical plate. could be a wiring issue, but I doubt it. I am saying that based on my experiences. I have only seen a few wiring issues on so many problems.

But me personally I would want to run a short test with a DAS to see what codes came up. I dont trust autozone reading codes on a german car. alot of times there codes are different then the actual codes that come up.
 

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Discussion Starter #10 (Edited)
Thats a great thread, esp the write up by Gilly on servicing the 722.6. I am ready to tackle this job myself and change out the conductor plate.

Anyone know the part no? I tried to buy one from Autohausz but they need the specific part name or part no.
 

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Discussion Starter #11
cyeung65 said:
BTW - seems to go into limp home when <80 C engine temp. When I get her warmed up >80 C, has not gone into limp home.
Ran the experiment again, started cold after sitting for a couple of days, and it is in limp home mode with all the warning lights on.

Warmed it up out of gear to over 80 C, shut it off and restarted. No more limp home mode, just the CEL light. Drove it around the block, drove fine.

If it is a speed sensor failure - why is it intermittent?
 

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Discussion Starter #12
Streetglower said:
normally when the trans goes into limp mode and your CEL is on, usually there is faults in the ETC. and they usually have to do with either the speed sensors or starter lockout, etc... My guess is you may need a new valve body or trans control unit.
Anyone know where the transmission control unit is located on the ML?
 
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