w210 driver's seat goes forward but not back - PeachParts Mercedes-Benz Forum

TomAllen · #1 01-20-2011, 01:37 AM

I bought the 98 E320 4Matic wagon a couple of weeks ago and it's a step up technologically from my 126's. In the last few days the seat stopped moving back with the switch but still moves forward. It moves both ways using the memory button, so it's not the motor. This is inconvenient but not a show stopper but what if the memory function fails? My wife drives the car too and she's short. I'm not.

The switch problem on my 126 can be fixed for no money and an hour's time by pulling the switch, dismantling it and cleaning the contacts. Not so the 210.

I pulled the switch and opened it up to find a circuit board with all the seat and steering wheel switches soldered to the board. The board also contains a bunch of diodes. I checked the fore/aft switch with an ohmmeter and it checks out OK. So now what?

The size of the wiring, on and to/from the switch, makes me think that there is a controller box somewhere that handles the motor current and that it may be at fault. Anybody know about a controller and where it is?

Thanks a bunch.

Tom Allen

mbdoc · #2 01-20-2011, 08:44 AM

Have you tried running the seat forward until it hits the front stop & then holding the switch in that direction for 2 more seconds for the seat computer to learn where the front stop really is?

TomAllen · #3 01-20-2011, 06:20 PM

Well, that was an easy fix! Thanks for the quick reply.

How did you uncover that? Is is part of a pattern of re-syncronizing assorted stepper motors?

--Tom Allen

dieseldiehard · #4 08-29-2015, 09:56 PM

Quote:

Originally Posted by mbdoc

Have you tried running the seat forward until it hits the front stop & then holding the switch in that direction for 2 more seconds for the seat computer to learn where the front stop really is?

OK, well I was just having the same symptoms on my '99 E300 diesel, did a search and here I thought I found the answer but after trying the hint (hold the button down for 2 or more seconds) I regret to say it didn't fix the problem.
However after a while I tried pressing the memory buttons, and after the seat was all the way forward pressing a memory button the set moved backwards! but pushing the seat button backwards still makes the seat move forward, there is no backwards motion unless using a memory button. This leads me to think it has to be the seat switch, not the module. But what do I know, I haven't the manual and without a wiring diagram I am not going to mess with it.
So tomorrow I will take the car to my friend Jureck at the MB Garage where I worked a short time in years past. He is factory trained and very experienced with electrical systems. These days a lot of mechanics have a tendency to try swapping modules or something simple, hoping that fixes the problem, they are what I call "shotgun artists" - I've seen a few of them before - they are either too lazy or incapable of figuring out a technical problem by actually reading the FSM and using their grey matter. Jureck is not one of those individuals.

I will admit though, I hate taking door skins off anything that came after the W123/126 chassis

I'll report back later on what the issue on this crazy door is!
Damn 210 stuff can drive you crazy, its just that this car is a really strong running diesel and gives great mileage (and I had the trans rebuilt last year)

- O/W it would have been gone a long time ago

DDH

duxthe1 · #5 08-30-2015, 12:50 AM

The different switch funtions are voltage coded by differing resistors in series with the various switches. When a switch gets dirty its resistance goes up and gets recognized as a different switch. A new switch pack will fix the problem but try cycling the switch back and forth quickly a dozen or so times. That will likely clean it enough to regain the screwy function.

engatwork · #6 08-30-2015, 07:50 AM

Thanks for the heads up d in regards to what is going on with the switch. On my 98 E300 the back part of the seat moves forward/backward in opposite direction in relation to switch position but won't go back unless you select one of the memory positions.

dieseldiehard · #7 08-31-2015, 11:57 AM

Quote:

Originally Posted by duxthe1

The different switch funtions are voltage coded by differing resistors in series with the various switches. When a switch gets dirty its resistance goes up and gets recognized as a different switch. A new switch pack will fix the problem but try cycling the switch back and forth quickly a dozen or so times. That will likely clean it enough to regain the screwy function.

Tried clicking the sw a number of times to no avail.
The expert (factory trained) mechanic looked at it this AM, he confirmed its the switch, saying its pretty common.
He tried moving the seat with the ign sw off, then on. It behaved good with the sw off, but badly with the sw on. He said the seat module "brain" uses stored seat settings when the ign sw is off, but when the key is sw on the sw operates direct and thats when it it was screwy. Something to that effect. Memory buttons always worked, just the seat bottom position button was always making the seat go fwd, not back.
This could actually be a big problem, for example if someone trying to make the seat go back wound up getting his legs smashed up against the dash and went into a panic mode, not trying the memory buttons instead calling 911 or something - don't laugh its probably happened!
So I just received a switch I got on eBay for this purpose, its tagged "working" so cross my fingers and hope a $15 switch does the job and lasts a few years.