Had our 2000 ml320 flatbeded in the dealer today. My wife was pulling away from an intersection making a left turn when she said that the trans would not shift out of first. She could not go over 10mph. No warning lights on. Ets light has come on several times before and I was going to advise the service writer at the B service, which I will have performed now that the ml is there. The dealer called back later that day and said they found no soft or hard codes of any kind and was there a possiblity that my wife could have engaged the low range 4wd. I asked, she said no. The tech at the dealer roadtested and all is well. Any ideas? BTW the ml has 30,000 miles on it at this time.

The normal problem causing this is a part inside the transmission called the conductor plate. It's a part that enables the transmission control unit to gather rpm data and also control the electronic shift valves. But they should have some codes associated with this failure, usually the problem is with one of the rpm sensors and they will have codes for one of these sensors.
The statement about if the truck could have inadvertantly been shifted into low range makes no sense; first, the truck has to be put in to neutral to do this, secondly the truck would still upshift in low range. I wonder if they had a fault code for the low-range motor. There is a postion indicator inside the low range motor, and if the position indicator would fail it may put the truck into limp-home mode. I have replaced a number of low-range motors as well, but my first suspect would be the conductor plate.
I'd be suspicious about the "no code" observation.

Gilly

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gilly, do you know how much it costs to replace the low range motor? I have a similar situation that the transmission won't up-shift and the low range indicator was flashing at start. It only happened once and now it is driving fine. I don't want to get stuck on the highway with the same situation.
thank
steve

Steve,
Probably a few hundred bucks. Mostly the parts cost, labor isn't that bad to do it.
You don't say what year it is; even though they look pretty similar, there are lots of internal changes.
If you have an earlier model, you may have a warrantable problem, because there is a recall or service campaign (can't remember which) for the transfer case control module, which can cause this low range light coming on for no reason. I'd ask the dealer if they can check the service history with Mercedes (called a VMI, vehicle master inquiry) to see if there are any outstanding campaigns on your truck, that is, campaigns that are not yet done.

Gilly

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Gilly , sorry for the slow reply but I have been off line for awhile.
Dealer did find a code 065 & found an intermittent failure in the trans control unit signal to transmission. They had to order one , which took one day. Could not get it to work , order another. This unit worked . Performed B service , on rode test BAS light turned on. Found codes C1140 & C1504. They identified slight play in steering column causing steering angle sensor to loose memory. Replaced steering coloumn with steering angle sensor . Cleared all codes & roadtested. Found all functions OK.
Also replaced right front filler panel (plastic). All parts & labor at no charge. A loaner car was offered but not needed. Was satisfied with dealer.