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Discussion Starter #1
While I was working on my mirror, I thought I check the seat switch group on the door. I was told by MB dealer 2 years ago that the problem was due to this switch but didn't bother me much as I had 3 good positions memorized. I also found on these forums other complaints about the same switch and how some people succeded in cleaning the buttons themselves as they transmit digital signals and are very sensitive. So, as I like to work on my car on anything that can be home fixed (or worth trying) I gave it a shot.

I disassembled the damn switch, and started measuring the voltages the 5 buttons produced when actuated. There are 2 types of buttons there a group of 2 and a group of 3. The 2 groups produce different voltage levels. But the problem is that all those voltages were very consistent through lots of actuations withing their group. So there are 3 identical working buttons and 2 identical ones. This is not erratic to me! So this is not what causes the adjustment to malfunction which means that the MB dealer wanted 400 euros for a module which was not broken, and that the other guys on these forums did not have the same problem as I have.

Anyway, the reason why the door control module received erratic voltages from the switch was the connector at the control modules, the one that comes from the switch, which is easy to recognize by the blue and red wires. All I had to do was re-seat this connector and that did it. Works like a charm now! Oh, my wife will be very happy! :)
 

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You are a very lucky man and your wife should love you just because of that.

These switches are not transmitting any voltage......how could you do all those seat movements plus the three memory location with just four or five wires?

if you look at the wiring diagram it shows that all the switches when activated are going low - almost to ground. But each of them, for all the seat movements have a resistor in their circuitry. For each seat movement/direction a resistor with a different value.

So if you are trying to move the seat forward by pushing the seat button forward the electronic control unit for the seat recognizes the specific resistive value and turn on the right seat motor which moves the seat forward.

You saw those tiny micro switches in the switch block at the door, if those micro switches are getting dirty and making no or bad contact the assigned resistive value might be changed and the seat behaves irratic.
 

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Discussion Starter #3 (Edited)
Sorry about that and thanks for correcting me. Of course I meant resistor levels when measuring them. But in order to have a resistance, a curent/voltage must pass through. This is where I was wrong.

About the switches in the door, I saw many switches in my life and these do not seem at all tiny (they are quite big) or sensitive to me. Plus they are not all mounted in the same direction which means the dirt cannot deposit in the same way on all of them. They produce a distinct "click", even more profound than the touch buttons used in VCRs which are mostly never defect. This is when I said to myself "is this switch block really the cause?". Lets check it on the car, where it behaved as before (erratic) until I reseated the plug in door control module.

I already knew the seat control module was ok as the seat obeyed the commands from DAS.

Anyway it is very easy to test this switch block. Each button has its own resistors so there are many identical resistors which probably do not go mad in the same time. So if one is using a multimeter it can be easily established which buttons are out of line.

Thanks for your reply!
 

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Discussion Starter #5
Must I dismantle the door panel to check seat adjustment swich for dirty? Funktion for up and down doesn't work.
Yes, that thing must go off and then with just a few plastic clips you can inspect the switch, the module and most importantly (at least in my case) the connection (plugs) between the 2. A contact spray might help also.

To remove the door panel: window open @max, 2 bolts on the bottom of panel, 2 in door handle, 1 at the door opener handle and then the classic plastic clips.

Good luck and keep me posted if it worked for you too.
 

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Yes, it was dusty contacts. It would be very useful blow out the contacts with compressed air time to time, and spray it for better contact. And use it here and there also.
Thank you Ikeakayke!
 

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Hi Guys, I have 2004 G500 and have the issues with the seat control for a few years. At some point I purchased the new seat control panel ( with buttons) and check to see if the issue comes from it, I figured out the seat control pabel( with buttons ) is fine. The problem is the connector that connect to door control module. The connector pins are a little corroded. When I spay contac cleaner it works for a few weeks or month or two and goes bad again. I also figured out that sometime when you play with buttons a little bit by moving back and forth you can make the seat move back ( hard to find the right force and angle, but possible). Solution for me was always the memory buttons. Just clean all the connectors move your seat all the way back and set the seat memory.
Real solution is to change the door control module (if the conectors both male and female are somewhat corroded) along with conectors ( which I doubt you can find any) or the whole wiring if you are willing to deal with that headache.
I haven't tried the that solution mentioned above ( service bulletin) that need to add additional length to the wire to add some additional resistance, maybe it can solve the issue, However when you see a corroded conectors you kniw for sure that the issue must be solved before trying anything else.
If you have any thoughts or have any information about that service bulletin please let us know. I am sure there are a lot of people have the same issue with the seat control.
 

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Corrosion in seat controls that are door mounted may be related to water intrusion, e.g. open the door with a lot of rain. However, corrosion means resistance. A product used in avaiation called CorrosionX may help. Not a solution, but a band-aid. Once this confirms the resistance is the problem, then solve the problem the right way.
 
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