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ml 320 transmission computer

33K views 16 replies 11 participants last post by  Noodles 
#1 ·
My first post so bear with me. I have a 1999 ml320 with 114,000 miles. I purchased the truck used, about 5 months ago, with 108,000 miles. Carfax records show that the truck was dealer maintained up until March of 2007 and also indicate a transmission fluid flush at 99,000 miles. Recently the truck has been going into limp home mode, and only goes in 2nd gear. If I
turn the truck off, and then back on, it drives fine for a while, but eventually
goes back into limp mode. Generic obd scanner (autozone) gives a code of p0700, transmission control module. I took the truck to the dealer for diagnosis. They told me that the computer pointed to a problem in the valve body and that they could replace it but it might not solve the problem. They reccommended that I replace the transmission and ETC control module. ($7,889.22 +tax). WOW, (I said it louder than you). There is a merchant on Ebay who has remanufactured ml320 transmissions (tranzparts). According to the dealer, if I buy a remanufactured tranny, the computer that I have will not work with it. The dealer says that the ETCs are married to the transmission that they came with. He says I would have to buy a new computer and have it programmed by them. Is this true? The merchant on Ebay says it is not true. I know he just wants to sell a remanufactured transmission but you would think that since they rebuild them, they would know and would require the ETC be returned with the core if indeed they were inseperable. Any thoughts or suggestions would be appreciated.
 
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#3 ·
Check your transmission fluid level and your battery/charging voltage, which are the basic steps you need to do first, before going to the MB Stealer.

Get a second opinion, the TCM is just a transmission controller that can be updated without the need to replace the ETC on ML's. Transmiission controllers are known to fail if the battery voltage is too low (in many vehicle brands, not just MB). The battery/charging voltage gets even lower when you try to start your vehicle, so the TCM may not be able to initialize correctly, so you may want to check your battery/charging state. If it is old and under specs, change it first.

Now you have a 1999 model, which had so many design and quality part issues/problems that Mercedes will not work on that transmission at all. They will replace it with a newer updated one, which may require so many other updates that they can string you for a lot of money..

Though what you need is an honest expert mechanic who understands MB transmissions and the electronics.

A well trained honest mechanic will understand/diagnose your transmission and electronics and find what is the real root of the problem is. they will not just change transmissions and controllers blindly.

Hopefully it will not be your transmission... Though ML's are known to have a whole set of issues (earlier and late models), and all of them are expensive with the MB Stealers...

AC
 
#4 ·
Code P0700 relates to the wiring harness that runs from the transmission computer to the transmission. Absent the fact that the harness is actually damaged, what this means is that the electrical plug at the transmission is giving a false signal to the computer, because it is possibly contaminated with trans. oil.

Read the PDF below and it will giveyou a good idea of this ongoing problem because of a faulty O-ring on the plug. If there is no oil contamination at the plug then I would say that you need to have the conductor plate changed, which is attached to the top of the valve body.

You do not need computers, or a valve body or a transmission.
 

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#7 ·
i think im experiencing this problem now, i have codes 0700 and also 0715 pending and went into limp mode earlier today. i notice a light covering of oil on parts of the under carriage, my question is this. exactly where is this plug located and what parts would i need to buy in advance to attempt to fix this? its very cold outside now so i just wanna make sure i have everything i need before i start anything, thanks in advance for any help
 
#5 ·
Thanks Solidjake, AC_ML, and 43sqd for your responses. Thanks to this forum I have tried most of your suggestions. The charging system is O.K., the tranny has been serviced twice in the last 2 weeks by technicians attempting to diagnose the problem, so the fluid is new, and before i took the car to the dealer, I did the electrical connector guide replacement myself. There was contamination in the female side of the plug so that when I sprayed it with electrical connector cleaner and let it drain, it ran out black. After spraying it 2 or 3 more times it finally ran out clear. I dried it with an air blower before reconnecting it. I took the truck for a test drive and it drove well. It did not go into limp mode within the first 25 miles of stop and go driving where before it would go into limp mode within 5 miles. Just as I was about to declare victory, limp mode. Thats when I decided to take it to the dealer.
But 43sqd got my hopes back up when he said P0700 refers to the wiring harness. Even though I cleaned the connector at the transmission and also the ones connected to the computer underneath the dash board, is it possible that the wiring harness itself was shorted out by the oil in the plug and needs to be replaced? No one has ever suggested that. It seems worth a try considering the alternatives. But how do you replace it and where can I buy one, besides the dealer. Is it a DIY?
 
#6 ·
Be resigned to the fact that you will have to go to the dealer and get the correct parts. Don't start shopping on line for these parts since they are vin specific.

Print out the technical bulletin and go to the parts dept. at the dealer and ask for the repair kit for this problem. The part number on the bulletin has probably been changed to a new number, but I do not have it. You will just have to be guided by what M/B tells you.

Before you go there, remove the 13 pin plug again and inspect for more fluid at the connector. Also strip the wire loom from the harness and inspect and clean all wires. Check for any softness at each wire. It's obvious that the problem lies at the plug or the wiring at the plug, so investigate thoroughly before purchasing anything.
 
#8 ·
The part that usually leaks is the 13 pin connector which is on the right side of the transmission. If it is found to be leaking, remove the connector and spray both ends with Brake Cleaner and then blow dry with shop air. Then take it for a test drive to see if that clears up the problem.

If it does then go to the dealer and purchase the connector and related seals.
 

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#9 ·
... The dealer says that the ETCs are married to the transmission that they came with. He says I would have to buy a new computer and have it programmed by them. Is this true? ... Any thoughts or suggestions would be appreciated.
You have found the number design problem with the 722.6 transmission. A simple O-ring failure can lead to thousands in repair cost.
 
#10 ·
i found some oil in the connector and cleaned that. i cleared my codes (0700 & 0715 pending) and tried to drive it....it seems to take a second for the gears to engage when shifting from park into reverse or drive and the shifting is really erratic. the most common problem is the 1st to 2nd shift - with normal acceleration right before it SHOULD upshift the rpms get a sudden burst then it shifts. didnt really get to check the higher gears as i was hesitant to take it out on any roads where i can go fast enough, i just been stickin to driving around the nieghborhood in case somethign went drastically wrong. so my question is now that i read the codes again, the only thing i get is 0715 pending again, which i read could be conductor plate issues. is there anything else i should look for or try in order to isolate the exact problem?
 
#11 ·
Get the connector replaced.. at MB it is less than 20 dollars. I have actually had good luck with the dealer here in CO.

I explained that I wanted to perform the work on my own ML to teach myself.. and they were more than happy to give advice. That particular connector (I was told) has a washer on it.. the new ones are BLACK (from many updates). If you remove the connector and you see any color washer (other than black), you need to replace it. They told me that since 99 models...they have used white and red rubber washers.. black is the 'new improved' one.

This was from a pending P0700 code and random cold weather limp modes. Also.. if you happen to get stuck in LIMP mode.. there is a moving solution (without having to turn the car off and on and cross your fingers). When you start off (limp mode).. let the car get up to speed (say 40-60mph)... move the drive selector to N and back off the gas pedal so the RPM's drop down. Then move the drive selector back to D. You will now be in a higher gear than Limp mode will normally allow. (And sounds better than a whining engine).
 
#13 ·
I'll be receiving a reman trans and a new control module on Monday. The '99 ml430 is shoved aginst the wall, it's cramped, and I'm tired. Does anyone know where the module is located and does it have a pigtail, or a modular plug at the tcm itself? Thanks anyone.
 
#15 ·
HAD THE SAME PROBLEM ON MY 2002 ML500 GOT CODE P0720- OUTPUT SPEED SENSOR CIRCUIT AS I REMOVED THE PLUG TO THE CONDUCTOR PLATE TRANSMISSION FLUID CAME POURING OUT. I PROCEDED TO CHANGE THE CONDUCTOR PLATE PLUG,O-RINGS,FILTER AND FLUID. DROVE FINE FOR 3 DAYS THEN WENT INTO LIMP MODE AGAIN I REMEMBER HOW FLUID CAME POURING OUT THE CONDUCTOR PLUG SO I DECIDED TO CHECK THE ETC (TRANSMISSION CONTROL UNIT) UNDER THE DASH BY THE GAS PEDAL AND IT WAS FULL OF TRANSMISSION FLUID I COULD NOT BELEIVE THAT TRANSMISSION FLUID COULD TRAVEL FROM THE PLUG ON THE TRANSMISSION UP TO THE COMPUTER. SO I DECIDED TO REMOVE THE TRANSMISSION COMPUTER CLEAN WITH ELECTRICAL SPRAY ALSO THE TWO CONNECTORS LET DRY OVERNIGHT,RECHECK AND CONNECTED IT BACK UP NOW DRIVES LIKE A DREAM ALSO HAD TO DO ADAPTIVE RESET AND CLEAR CODES . HOPE THIS HELPS SOMEONE,
 
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