W212 Gear Selection Problem( the gear automatically shifts to P from N, R or D)

I have a mercedes benz e250 cdi 4matic which calls w212 and whose model year is 2012. I have a problem with the gear selection which is that the car automatically (by itself) shifts to P from N, R or D while moving at 0 to 8 km/h or not moving. Firstly, I went to a mercedes authorized service, and they checked the car and they updated the gear selector and they said that it is okay, but the problem continued.
1)It has no fail code so it shows that everything works properly.
2) Generally, after the car goes 20 kilometers(11 miles) or higher, i stop the car and then again start and then the problem is existed. In other words, when i start the engine again the problem is existing.
3) The gear shift to p from N,R or D three or four times. For example, I shift to D or R or N but the gear automatically shift to Park then again i shift to D or R or N but again the gear automatically shift to Park Then, the gear is not automatically pass to Park. Therefore the car works perfectly after making the shifting to p three or four times.
After that, i went to another mercedes authorized service, serviceman says that the problem can arises from left door lock or ignition. It makes sense, because when the key is removed or the left door is opened, gear shifts to P.
My observations and experince are that when the gear shift to P, it has no warning like door is open or the top light is open. I use my spare key but the problem has not been solved.
I hope you can help me. Sorry for long writing. Thanks you a lot in advance.


user profile image
CarCarePros made a comment.
1 year ago

On the left side of the automatic transmission is mounted what is called inelligent servo module (ISM). It receves signal from the direct select (A80) module which is your gear selector on the steering column. The ISM gets electrical signal from the DIRECT SELECT module and selects the appropriate drive. The signal has to be transmited via the engine control unit (ME).

When power is turned off at the ECU/ME the ISM automatically shifts the car into park. Like if you simply remove the key without put the car in Park first. You will notice that it goes into P automatically.
I think the problem here could be a bad ISM module or a loose contact somewhere. To narrow it down you will need somone who has Star Diagnositc and drives the car around while looking at live values. You want to check if the shifter module is sending the signal for Park (which I doublt) or if the ISM is loosing communication (which means it automatically goes to park).

Sorry I can't help much more. I would love to hear the solution to this problem. Please come back and update. This is not a common problem and as you have already learned it will require a tru Mercedes Benz specialist to figure out.

user profile image
Matej made a comment.
4 months ago

Hi i have this same problem with my W212 and went to Mercedes dealer yesterday. They have not found any error message via diagnostics. As this is rather a rear problem they reached mother factory in Germany for advice. Based on their database and my VIN their recommend to change EZS or simply said the module where you put a key. This may but as well may not solve the issue. I changed keys as well so there is not the problem. I hope by changing EZS problem will be solved. Mercedes prize for this operation is 900e material + 100e work so i am having my mechanic to order it via internet and install. Saving couple of hunder euros :) Will keep you updated if that helped.

user profile image
Matej13 made a comment.
3 months 2 weeks ago

Ahoj, my problem is resolved and it costed me 1,070e :( All was caused by wrong EZS - most probably there is problem with some electronic parts and glue used in it. After longer ride glue heats and creates electronic problem. That problem cause EZS is not seeing key in ignition and therefore it automatically turns into P. I explored few options how to change the EZS. Repair is the cheapest option (they keep data in EZS so re coding of key is not necessary). For me was too far to go to next country for few days (company is in Czech republic and i am from Slovakia). You can as well to take it out and send via post which would make my car out of service for 1-2 weeks which i did not want + extra cost for taking it out and installing back. Another option is to buy second hand EZS but only Mercedes dealer can code it to your keys plus you need to change other parts as well like steering lock, etc. so they match to new EZS. That looked too difficult to me and extra cost. Therefore i decided to change it at Mercedes dealer. EZS arrived in 4 days with new coding key and replacement too them 1,5 hrs. Hope my experience help to someone ;)

user profile image
MercedesMedic made a comment.
3 months 2 weeks ago

Glad to hear that it is solved. Thanks for the update. 


Add new comment

The content of this field is kept private and will not be shown publicly.