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  #1  
Old 03-23-2015, 05:45 PM
mustapha63701
 
Join Date: Sep 2004
Location: Cape Girardeau, Missouri USA
Posts: 4
1998 ML320, I decided to test functionality of the "Low range" and now it is stuck li

Hello everyone,

I have a 1998 Merc ML 320. The vehicle was driving (shifting) just fine, until I decided to test the "Low Range" button. In doing this, I first read the instructions in my owners manual. As stated, I placed the transmission in neutral, (the vehicle was on a level, paved surface, with engine idling normally,) I then pressed and held the "Low Range" button. The "Low Range" light flashed thrice, then stayed on. So far, so good. I did not drive the vehicle. Satisfied that "Low Range" must be functional, I then placed the vehicle into neutral once again, then pushed the "Low Range" button, once more. The light went off. I thought all must be well, and I was pretty happy that I had a functional "Low Range."

The problem?! Well, after doing this seemingly uneventful test, I then decided to drive somewhere and to my horror, the vehicle would not shift out of low-gear! I pulled over and tried to replicate my earlier "Low Range" test. Nothing doing! The "Low Range" light would no longer switch on, and the vehicle is stuck, presumably, in limp mode? (The engine is doing 2500 rpms, whilst the vehicle is traveling at 25 mph!)

I called Plaza Mercedes in St. Louis and spoke with someone in their service center. I mentioned the problem and was in turn asked how long it had been since the vehicle had been put into "Low Range." As far as I know, it had been years! The technician stated that likely, if I just tapped on the electrical motor with something, (also cleaning the electrical connections,) and cleared the transmission computer codes, things should be OK. I took the vehicle to a friends shop and he did all those things, yet the codes would not clear, and the transmission is still in limp mode. (P0700, which I think is a Transmission Control System/wiring-connection related code?) I was told that whilst all else looked good, the motor itself appeared to be corroded, and that I should purchase a new one.

Having said all this, I would very much appreciate it if you folks could help me with the following questions:

1. If the electrical motor was non-functional to begin with, is it possible that I could have "fried" something (i.e., transmission module,) when I tried to engage the "Low Range" button? Or is there a simpler answer?

2. Also, is it possible to test the electrical motor, to ensure that it is functioning properly?

3. Is it a relatively straight-forward, (simple) process to clear the codes from the transmission computer? (Would codes need to be cleared from all computers?) Or is there certain Mercedes-specific steps that must be taken, to clear codes. (The relevant code in this case is P0700 Transmission Control System, MIL request.) The other codes are: P0400 EGR, P0141 O2 Sensor Heater Circuit Bank 1 Sensor 2, and P0154 O2 Sensor Circuit No Activity Detected Bank 2 Sensor 1.

4. Are there other "simpler" repairs that I could do, prior to purchasing another electrical motor?

Thank you very much everyone, for your time and trouble in this matter. I'm very familiar in general with older Merc vehicles, (i.e. W123, W124, W126 chassis Mercs, etc.,) but this is my first W163 ML.



Mustapha Stokely

1995 (W124) E320 wagon
1998 (W163) ML320 SUV.
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  #2  
Old 03-31-2015, 12:44 PM
mustapha63701
 
Join Date: Sep 2004
Location: Cape Girardeau, Missouri USA
Posts: 4
Hello,

I see today that there have been 121 views and zero replies and well, I suppose sometimes it just happens. Since posting my originally query, I was able to find something that seems to apply to my particular situation. I will cut-and-paste the relevant content, in the hopes that it might be helpful to another Merc ML owner.

I quote: "This is a common problem on these older model ML vehicles as I have run into several times before. What usually fails here and causes this to stick in low range like this is the electric shift motor on the transfer case.

It can fail to where it wont shift into low range or fail to where when it is shifted into low range it wont shift back out.I have also seen these motors fail on the transfer case to where they will shift into low range on their own while driving without pressing any buttons.

In some cases you can put the vehicle into neutral at a stop or very slow rolling speed (less then 3 m.p.h.) and push the low range button several times giving it a few seconds between presses.This will sometimes correct this problem here.In other cases the shift motor will have to be replaced.

I have run into a few of these where the transfer case control unit under the center console fails and can cause this,this isn't as common as the electric shift motor on the transfer case though.

So if shifting it back and forth repeatedly a few times does not correct this problem then most likely the shift motor on the transfer case will have to be replaced.These can usually be purchased at a Mercedes dealer as well as some after market parts stores.They can usually run around $150,simple to remove and replace,the bolts are removed that hold it in place,the electrical connector removed from it and then it can be removed and a new one installed.

You will also have to have the fault codes cleared out of the transfer case computer with a scan tool that can communicate with the transfer case computer."

There you have it, hopefully this will be my solution as well.

Mustapha Stokely
Cape Girardeau, MO 63701
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  #3  
Old 04-22-2015, 05:20 PM
Senior Member
 
Join Date: Dec 2002
Location: Visalia, CA
Posts: 379
I do think you're on the right track with the transfer case shift motor, and yes, sometimes you can knock them around a bit to get them to move again. This is rarely a "Fix" though, it is still best to replace the motor before it sticks again.

Mainly what I wanted to mention is that from the code you posted, it seems like you are only talking to the engine control computer, not the transmission one. If that's the case, you might want to see what your options are for dealing with the trans control unit, as it is likely to have both useful info and codes stored. You'll want to clear those codes after the repair. There may be a learn-in procedure for the motor also, I don't recall of the top of my head.

MV
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