I've read and researched until my eyes have closed. I have the same problem originally stated in this thread.

2013 ML350 decides at times it will not shift into gears after a while... After scanning a few errors that came up states the ISM was bad so it was replaced. Worked for about a week before going back to what it was doing.

Replaced the Auxiliary Battery even thought it's voltage is around 12.8v

Replaced Main Battery with new Champion AGM battery even though voltage was fine.

Took voltage reading from Alternator and no problem there.

Replaced FOB Key battery (after 4 energizer batteries kept getting "Replace Battery" message. Switched to Panasonic and message went away. Vehicle drove fine for 2 days now back to it's same.

Scanned again and the following code comes up - P172A00 - The Direct Select Lever is Faulty.

Additional code U1420 - CAN communication with the control module "N80 (SCM/MRM)' is faulty

Can't find anything that explains or deals with this code however almost convinced this is the problem.

Can anyone shed some light here??

 

The code says the direct select lever is faulty. Do you plan to replace it?

Diagrams and descriptions below. SCM is steering column module.

 

Either do it myself or at least know what the issue is in order to get it fixed.

Although now it brings the question of "Would the "The Direct Select Lever Fault" also cause the subsequent error code "CAN communication with the control module "N80 (SCM/MRM)' is faulty" or vice versa?

At this point seems to me like changing out both would be the safe bet.

 

Having finally received the Steering Column Module and chasing down all other issues I have finally fixed the problem.

I will however state that my case was a bit different as I had multiple codes that required replacing various things. For example: Normally this problem occurs when your auxiliary battery or primary battery are going bad. In my case neither battery was retaining voltage so obviously that's where I started. The voltage from the alternator was within specs however the batteries were faulty. New batteries were installed. That resolved the first round of issues.

The next issue was the ISM Module as I was also receiving faulty codes. This is not an easy fix to do yourself unless you have the proper equipment as this module requires coding the vehicle VIN. Nevertheless I did replace it and code it which took care of the ISM Fault code.

Last but not least (and was the reason I posted in this thread) BIG thank you to Chasis for confirming my belief as well as pointing me in the right direction to find the part - the SCM/MRM fault code.

Once the part arrived and I replaced it the remaining codes were cleared and the vehicle has been running like new.

Like I said, you really need to pay attention to the trouble codes and a simple scanner will not help. I own various high end scanners including a Zeus with updated firmware and software. I hope this post and thread will help anyone with this issue.

Last but not least having done the work myself I saved thousands. BUT this is not for your average "I change my own oi & spark plugs" type person for the ISM module I mean. Everything else is a walk in the park.

 

Well done! Thanks for posting the results for the benefit of others.

 

I’m a little confused by the result here... Was the final issue the SCM or DSM? I was having the same issue, replaced both batteries and it went away for a while. Just got emissions done and was not able to shift out of park.
After seven shut down and retries, got home, scanned the car but there are no codes being thrown. Now I can’t replicate the issue.
Is there a common culprit outside the auxiliary battery that may not show in the OBD? Or, is scanning during the mishap a must?
Hoping to get someone else’s expertise before buying a DSM on faith.
Thank you!
Joe

 

If replacing the batteries doesn't resolve it - it may be the lever itself. Keep monitoring it and checking for faults next time it happens.

 

I am curious as well as I have been having this "stuck in park" problem.
one thing I determined was that it doesnt happen if I insert the key into the switch rather than rely on the push button start. This may seem strange but I did several tests. I checked the AUX battery, even using a different much stronger battery. what I found was that (almost) every time I get an error for Low Key Battery, I cant shift into D or R. So far this has only happened when the car was cold (-10 or more). I figured a weak aux battery but was not able to correct the problem using 2 different batteries and I tested my original at 12.3v @ -15. Main battery is fine too as my vehicle will start first crack even at -25 so i really dont think its a battery issue of any kind.
I put brand new batteries in the remotes and verified them at 2.9v+. both fobs will give the Low Key Battery warning when its really cold, but not every single time.
One thing I didn't try was to hit the button without my foot on the brake to activate the car, then pop out the button and start with the key.
so far as long as i start the car with the key in the slot then i can switch directly into D or R no problem no matter what temp.
I am wondering if the lock/unlock functions (which seem to work fine) are in a separate module than the Keyless Go functions. So maybe the AAM module doesnt boot up correctly when its cold and something else in that system doesnt sync up well and allow the ISM to function. I would be very curious to see if my ISM has any faults but I have not tested to see if my scanner even has the capability of reading that module. Assuming the "**** to drive" command has to pass through the AAM as part of verifying that the person with the key is in the car, but if the ISM never sees that command, or it comes back outside of a certain time requirement, I can certainly see the ECU making the assumption of "shift not completed" or something like that and logging a code. I havent worked on these cars so I'm really just throwing spaghetti on the wall here but i have seen my share of interconnected modules not always "connecting" correctly.
from what i have read so far, the AAM is supposed to have sensors (antennas) that pick up the key fob. if for some reason it picks up the module at initial start, then when starting the module looses just enough power to cause a firmware glitch it could do all kinds of weird things. All i know for sure right now is that i confirmed that with the key in the switch, my trans shifts every single time. I verified that it goes into gear just fine, then stop the motor, put the push button back in, press the brake, hit the switch, get the low battery, and it wont shift. shut off again, pull the button, start with the key and it works. at least for me.

 

I can rule out a fob issue. I was unable to change gears several times with the keyless go puck out of the ignition. Tried several times with both the key and the keyless go.
when the issue came up I tried scanning with my OBDII, the comprehensive Zennith. Nothing came up.
Has this been the case for anyone else? I would buy the shifter and replace if my fellow owners have had the same luck.

This is a big issue to me, I’m falling out of love with the brand. Talk me out of it, friends!

 

It seems like there is a steady stream of owners leaving the brand, judging from posts on the site.

 

or fewer and fewer diy’ers as the cars become more dependent on dealer tools we simply don’t have. The brand isn’t the problem, it’s the evolution of their automobiles imho.

I’m not attempting to futz with anything on mine when it comes to computer components, let alone my wife’s GLC. But when it came to my old w163 which is no longer with me, or my r107, of course I’ll roll the dice.

The people that are putting down 75k+ for a new, or slightly used CPO with a warranty Benz are not going to be frequenting these forums 😉

 

This is the exact same problem I had as described in the thread before this one titled "Modules." Just picked up the ML at the independent shop. They disconnected the "stereo" and the truck shifted into R or D just fine. Plug it back in and won't shift out of Park. This is after spending $1,000 on having the HVAC module replaced. So now driving around without Command, but the truck will shift out of Park. I have an appointment to take it to the dealer on Monday to get to the bottom of the problem. If they can get it working, I'm going to have them put the old HVAC module in and see if it still works. If it does, I'm going to take the new one back to the indy guy and get my $900 (cost of part) back. Even though the indy has a lot of great reviews and he has a ton of customers, I think his mechanics are just that -- not technicians. They seem to have a lot of older Mercedes in their service area. The place is very busy and you can barely drive in/out of it. Nice people, but I just think they don't know how to fix my problem. (BTW, both Aux and Main batteries are less than a year old.)

 

Keep us posted, please!
I was going to have it looked at when the dealer fixed the moldy air condition recall/warranty extension. Had to cancel my appointment.

 

I’m no mechanic but this seems like something that should be easily diagnosed via some fault codes, no?

 

I’m not picking up any codes at all, even testing when it’s happening. May be my scanner or me doing something wrong...

 

You would think, but it doesn't seem to be the case. The dealer is going to charge me $200 to diagnose the problem. Have an appointment for Monday morning.

 

Any update

 

Here's the update. The dealer said that they couldn't duplicate the problem while it was in their service department, but did find that the main big battery (under the passenger seat) "failed." It was under warranty, so I had the battery replaced. Everything was fine until a couple of days ago, when it again wouldn't shift out of park and all the warning messages came up on the screen. I talked to my service advisor at the dealership and they arranged through Roadside Assistance to have the car towed back to the dealership. And that's where it's been for the last day.
One interesting thing is that the tow truck driver happened to have an MB scanner with him. It turns out he has three Mercedes himself and does a lot of his own work. He hooked up the scanner and go codes for the HVAC module not communicating and the steering control module not communicating. Both these modules have recently been replaced (the steering control module twice). So, we'll see what they come up with. I'll keep you posted.

 

If you're having any battery related issues, and the truck doesn't like the voltage something is sitting at, it will tell you North Korea is about to launch a nuke in terms of codes. Hopefully the dealer eats the cost as they misdiagnosed.

 

Here's the usual scenario: Driving along and the message will briefly come on saying something like "Distronic Not Available" or "Lane Keep Assist Not Available." Drive home and park the car. Go to start it again, car starts fine, but all the messages come up the screen and the engine fan goes to its highest speed. Try to go into drive or reverse and nada. Won't budge. Still at the dealership. The service manager drove it home last night. I was hoping he encountered the same problem, but so far have not heard from the service advisor. I'll keep you posted.

 

Further update: The dealership couldn't get the problem to replicate. Worked perfectly every time they went to move it. BUT, good news, when they went to take it to the wash bay and calling me to pick it up, it wouldn't shift out of park, the fan went crazy fast, and all the warning messages came up on the screen. So now they're digging into it deeper. I have a gut feeling that there is either a loose or corroded wire someplace that isn't sending a signal to the different modules and the modules themselves are fine. Just a hunch. I will update when I hear from the dealership.

 

Next Update: Dealership called and said they have found the problem. It is the ESP/ABS control unit is not communicating when it is failing (not going out of park). My feeling is the other repairs I had (at an indy shop) were not needed. They are the steering control module and the HVAC control module. I feel they just misdiagnosed the problem to the tune of $2,000. I have the HVAC module that they replaced and the dealership to going to reinstall the old one and see if I have any further problems. My bet is that the car will be fine. I'm then going to take the new back to the indy shop and hopefully get a refund of $900. Film at 11 as things progress.

 

Thanks for the updates. What is the root cause of the ESP/ABS control unit not communicating? What parts is the dealer replacing to correct the situation, if any?

 

Bump. Just got stuck in the middle of the road. No errors thrown on mine.

 

Junior, you saved me a lot of time and expense! Thank you!!!

I have a 2013 GLK350 which started to not want to go into gear several months ago. The transmission fluid needed to be refreshed so I did that along with a transmission filter. Of course the problem persisted. I started researching and replaced the main and alternate batteries. And the problem persisted. I then pulled the P172A00 code with a Carly scan tool and purchased a new steering column switch assembly. As you said, that replacement was very easy and the problem appears to be resolved. Thank you again for this post, you really helped me! Dave