I had this problem, I couldn't find any information on how to fix it, but I was able to fix it myself, so I thought I'd post it here in case somebody else has the same issue.

How problem occurred:
Driver's head rest didn't lower (bad solder join on head rest motor, now fixed) so when seat was raised to let back seat passenger in, the seat got stuck because the head rest had jammed against the front windscreen.

The seat was able to be forcibly pulled down, but from then onwards the Lock Driver's seat error appeared on dash. The seat firmly locked in to place and all seemed well, but the error continued. Since the error remained, the electric seat would not work, neither would the steering wheel adjustment, and since I had convenience enabled - the wheel was stuck as high as it goes, or Bus Mode as my friends called it.

Cause:
My guess is, due to the way we forced the seat back down, it didn't do it's proper 2 step motion, eg: seat down, then back rest down. So something was out of order, and it didn't matter what I did electronically, it wouldn't reset.

The Fix:
Very simple to fix, I will do my best to describe. Firstly, I am working on a right hand drive model, I am not sure how this looks to a LHD, but I assume it's just a mirror image.

Fold the seat forward, and have a look underneath from the rear (you will probably need a torch). On the rail closest to the door you there are 2 silver parts I believe are connected with springs. The one closest to the engine I believe pivots and is used to raise the seat when lifted, the one closest to the rear was my problem. It simply had not moved to its correct position when the seat was lowered. All I did was push this and it rotated back to its correct position. There was some tension as it has a spring on it somewhere I think, but it was easy enough to move. I then pushed the seat back and all was well.

I apologise for my vagueness in description of the part, but if this problem does affect anybody else, I will see if I can snap a picture.

edit: see post below for pictures

 

Good find, Sam. I've had the problem with my seat not locking in place enough to trigger the switch so I usually just give it a good slam and that does it. It's only done it twice, and both time the slam seemed to take care of it so I haven't bothered to investigate further.

Oh, and BTW, I love the British words like, "you will probably need a torch." On this side of the pond, a "torch" is a burning flame, not a "flashlight". I would never take a "torch" to my car's interior parts!

 

this is great i ended up unplugging the computer under the seat and bridging the passenger seat motors to the drive to adjust the seat so i could be comfortable a picture of what to move will be really appreciated

 

Hi Rodney,
Yeh I tried the slam method a few times, but it didn't work for me. I wonder if the slam moves the part I am describing?

lol, yeh don't take a flaming torch in to your car. I had a similair problem when I visited the USA recently and was looking for sticky tape....."oh you mean scotch tape?" ... "um possibly?" haha, was good fun.

 

OK, so I quickly ran out of work and took some pictures. Sorry for the blurryness.

So the first picture, (IMG_203) is taken from behind the seat looking towards the front of the car (again, this is a right hand drive). It shows what I was trying to describe. The red arrow indicates the part I moved which got everything working again for me. The blue is just to point the similar looking part closest to the front of the car that I described in my first post.

My seat is now in working order, and at the time of this photo it was moved forward fully and tilted forward (not raised), so I assume my photo shows the correct position of this part in the seats current mode.

As I described earlier, all I did was push this part and it moved to it's correct position, it was not difficult at all - just hard to locate!

The second picture (IMG_202) was just to show more of the mechanism (taken more to the right than the first picture, if the seat wasn't there the camera would be taking a photo of just out the door - if that makes sense). It shows a bit more of the part and yes, there is a micro switch there that must have been what was triggered to say the seat was lowered correctly.

Anyway, I hope this has been helpful.

 

Good photos and write-up. I'll remember this the next time mine won't engage.

 

Wow!
about a year ago, my wife was driving and moved the drivers seat all the way up and forward to let someone in the back with plenty of room. When she unreclined the seat after the person go in, the seat was stuck in that position...I had to drive it to the dealer with the steering wheel in my chest to have it reset. I bet this would have fixed it....
thanks!

or should I say "cheers"?!

 

Cheers is quite correct in this situation

Hopefully this helps if it happens again.

 

Thank you I Am SAM you have saved me a lot of trouble.I read your thread and carried out what you sugested and it worked a treat,gave the backrest a bit of atug to release the headrestraint and everything went back to normal.Cheers.

 

Does this apply to passenger seat as well? My passenger seat headrest is stuck against the windshield and won't budge with controllers. Headrest is raised to the max. Someone help!!

 

Thanks for this brilliant tip!

Just sorted my'n, was scratching my head for a while till I saw this post.

 

hello,
this does not work on a w209 2008 clk350
the backrest seat position is controlled by a micro switch under and in the rear of the seat
gavinbr

 

hello again,

need to add to my comments previously regarding "drivers seat backrest not locked"
this is the result of a micro switch in-bedded in the seat cushion frame not being activated by a pall which moves down to make contact with this switch when the seat back rest is in a forward position, in doing so stopping the seat, the mirror and the steering adjustment from functioning.
there is a spring around this pall that provides additional pressure for this to take place.i guess it could come off in some instances and prevent the switch to work. as commented in a previous thread
however in my case a quarter had found its way down and lodged into the mechanism preventing the pall from making contact with the microswitch.
to get to the micro switch can be huge deal if your seat is stuck in a position that will not allow access to the seat bolts and or the seat cushion bolts. on my clk350 2008 w209 the seat cushion removal was the best bet it allowed you have complete access to the seat frame and motors. however if the seat is set in wrong position when it fails getting to the bolts is a night mare
in another note my wife always complained the seat wouldn't go high enough for her to drive properly we used cushions. well the quarter had lodged in the mechanism preventing this. with the seat back rest being lifted up and down caused the coin to penetrate further so blocking the microswitch from operating. getting it was no easy task.
For those who would want to, it is possible to disconnect the microswitch completely, it plugs into the seat controller, if mine goes again i will do this.
very frustrating why Mercedes would set this arrangement up, the number of posts over this situation is amazing mercedes shops are making lots of money with this repair

 

additional pics of the the seat back rest micro switches for the left and right front seats

In the left pic you can see the coin/quarter lodged in the gears

 

two more pics for the front drivers seat back rest micro switch control

please note the white plug in the seat controller this is the connection for the micro switch

 

Thank you for pictures. I located the culprit!! A quarter wth!!

 

 

In my case, in the upper right hand corner of the pic there is an aluminum part that broke (it has the metal spring attached to it). You can see the green sensor switch it pushes when it locks in place. I was able to reach under seat, push the switch, move the seat to back, then adjust the buttons on the door to get my seat in the correct position. For now, the seat is where it needs to be. I have a seat track replacement coming up soon. This is a working seat track, I have not removed mine yet.
**Update** I posted this in the wrong thread originally. Deleted and reposted here. I ended up finding the two wires connecting to that green switch (It's the top wrapped wire in the pic). Open = locked, so I just clipped the wires, and seat was good. The only thing that won't work is the headrest doesn't go down when the seat moves forward.
Leave it to Mercedes to reverse the switch function lol. If open meant unlocked, then this issue would only be "My headrest does not go down when I move the seat forward" thread.

 

Thank you so much!!!!! This was super frustrating! Your fix worked wonderfully. I think the cause in my case was the floormat sticking up the block the lever from moving.