TemjinX2

Hi Everyone,

If your like me and out of warranty and think its insane to pay $400 to replace a seat control module that shouldn't go defective in the first place. This is the fix for you.

Warning, i'm not responsible in any personal or property liability that may occur from the use of this post.


This guide is recommended for someone with basic knowledge of electrical wiring, such as splice, crimping..etc.... If you don't know the difference between + and - or never spliced in your entire life. I recommend you have someone with more knowledge do this for you.

Its for your safety and keeping you from frying the electrical components in your car.

With that out of the way.

Tools needed

scissors

heat shrink

30amp-40amp automotive relay

16-20 gauge wiring (stereo wiring)

18 gauge wire taps

18 gauge female connectors

18 gauge barrow connector

wire crimp

First, move the seat high and as far back as possible to give your self some room to work.

Since mercedes thought it was a good idea to keep most of the wiring live even when the key is removed, disconnect the battery.

Now on the front harness you will see two wires. One thats a solid brown and another thats brown/red.

Cut the solid brown wire, but give your self enough slack to be able to put a connect onto the harness end.




strip the solid brown wire and put a female connector to it. Make sure to heat shrink every connector. Next connect the female to the 12v input on your relay.

With that done, now you need a separate ground and 12v trigger for the relay. In this case, i use the 12v and ground from the cig lighter.

This way the seat control module will only turn on at the second key position setting and turn off when the key is removed.

I had some spare wiring around and used the wire taps to connect to the 12v and ground from the cig lighter. The other end of the wiring make you should strip and add a set of female connectors.

connect the female connectors to the relay. Connect the 12v from the cig lighter to the 12v trigger on the relay and the ground on the ground input on the relay.



Now get some spare wiring and connect one end with a female connector. Connect the female connector to the 12v output on your relay.


On the other end of the wire, strip it and connect it to the barrel connector and mate it from to the solid brown wire from the oem connector that you just cut.





now connect the oem connector to the seat control harness.

reconnect the battery.

Turn the key to the second position and see if the seat moves. Then pull out the key and see if the seat doesnt move. If its yes to both questions then you have been successful. If you got a no, check your wiring.

So far, its been working pretty good for me with no battery drain. I'll give it another couple of days and report back if there's any change.

Sorry i don't have more detailed pics, but i did the fix first before taking pics.

Since i had most the items laying around from other projectors, the total fix for me was $5.00 for the relay. Your cost will vary depending on what tools you have and what tools you need to buy.

aolsen

nice post. Would this fix work with the w203 C230? My drivers seat module went out a while ago, I havent fixed it, its in a comfortable position lol. Is the setup for the C32 the same as the C230? does anyone know if the C230's seat module entirely goes bad, or can it be fixed the way this thread explains?

splinter

You’re very good with the electronic tweaks. I tend to shy away from that stuff because I don’t want to melt the car.

I suspect the original design intent of the module was to permit seat and wheel adjustment prior to getting in the car. It’s indeed a useful feature, as I’m 6’3” and the Mrs. is 5’5”. There is no way to shoehorn myself in without first sliding the seat rearward. As a result, I purchased a few of ‘em.

If you’d care for assistance with your forthcoming heat exchanger installation, that’s right up my alley.

TemjinX2

the seat modules do not go entirely bad. The motor functions work, but the module never tells the ecu to turn off the power to the module, therefore drains the battery overnight.

I believe all the seat control modules between the different c-class sedans are the same. I'm currently using c320 seat modules in my c32.

TemjinX2

Thanks.



you can just change the trigger, for example you can change the trigger to the dome light, so the modules will be active when you unlock the doors. Just change the doomlight setting to maybe 30seconds so you have 30seconds of seat module power and then it'll deactivate or you can reactivate them by turning on the dome light.

I might take you up on the heat exchange offer. ..I'm saving so i can do the intercooler pump, radiator and exchanger all at once. I think it'll be great if we can setup a tech day and have everyone meet up and help each other out on there installs.

aolsen

good to know...My C230 has the power module for leaning and moving the seat up/down, but it manually moves forward and back. The first night I drove my car home, I fixed my seat into a comfortable position, and later that same night it stopped working.

C230 Sport Coup

Brilliant. A simple yet elegant solution to an ongoing common MB problem.
This needs to be a sticky.

TemjinX2

my fix is only for the battery drain issue...if the motors stopped working. Then its probably some wrong with the module itself.

c32used

TemjinX2

You are very resouceful and I to that! I am about close to ending of my extended warranty but you help remove the fear of lack of warranty on the C32.

Your the man!

TemjinX2

when your cheap, you become resourceful

c32used

[EDITED]I DON'T consider you cheap...personally I think you and I are similar and want to get the most for the money..

TemjinX2

lol...yeah..if the c32 wasn't so fast. I think i would get pretty annoyed with all these little things that tend to break before there time.

(for glyn)

i blame all on bosch.

mleskovar

Nice fix, bravo.

pshek

Mike,

Nice fix with the relay. Do you still have the SRS error message now? You might need DAS to get rid of that. Tech day might be cool.

TemjinX2

yeah i think your right. i'll probably have them remove it when i get a ecu tune.

Glyn M Ruck

I was about to ask if that was ANOTHER Bosch part

FrankW

damn Mike...coming to you for this if and when seat control modules die again after extended warranty is gone. lol

nice write up as always

MJ50

mike = mr.wires
drex = mr.zipties
jose = mr.monkey
frank = mr.vinyl
john = mr.track
phil = mr.testdrive

TemjinX2

i was just kidding...i'm not sure if its bosch or not. i heard they were manufactured by siemens.

TemjinX2

just as a update...i decided to clean up my install and move it from the cig lighter to a aux switch i rigged up to turn my car computer on and off.

I found out it looks like the red/brown wire continues to feed the seat control module even when the brown wire is off. Your going to need to cut the red/brown as well. You only need power from the solid brown wire to activate the seat controls.

Once i disabled the red/brown wire..i can turn the seat control module on and off via my aux switch.

c32jet

I have a few issues with my C32, the battery drain being one of them. Your post is great and I want to ensure I have all my info correct before I head out to radio shack and perform the $20 surgery.

Issue 1: Battery drain - which I believe is directly related to the driver side seat module as I have researched here on the forum. It is currently disconnected. The passenger side seat is still connected.

Issue 2: Driver side door does not lock with key. I figure this has something to do with the seat module being disconnected as it likely drives the IR receiver or something. The windows work (all) and so does the sun roof. Anyone care to advise on if this is the case? Each time I want to lock / unlock, I have to go to the passenger side door. On occassion.... have not figured out how or why, the driver side door lock 'does' work. I have recently replaced the batteries in the key.

Can someone help clarify my questions and pics below? Thanks all.

ps. really like the idea of fixing this for $20.

Pic 1
1. Where does this wire go / connect to? This thing is your connector yes? (A)
2. What color is this wire? Hard to tell in pic. (B)
3. Where does this one go? (C)
4. What color is this one? (D)

Pic 2
5. Where does this wire come from? Cig Lighter? (E)
6. Which connector from Pic1 is this? Is this the power source? (F)
7. Red Wire going into relay (G)
8. Relay (H)
9. Red/Black to relay (I)
10. What does this wire connect to? (J)

Pic 3
11. Which wire is this? (K)
12. Where does this go? What does it control? (L)

Questions:
Pic 1 (A) = Pic 2 (F) ??
Pic 1 (C) = Pic 2 (J) ??

TemjinX2

the seat drain issue and your locks are separate issues.

I don't know how to fix the door lock issue. I think someone in the c32 forums had a similar issue.

PIC 1

B = solid brown wire

D = brown/red wire

A= solid brown wire connected to the relay as the + input

The yellow connectors are barrel connectors with plastic tops, so there reuseable and you don't have to heat shrink. I used these since i had no schematic to work off and just figured it out on my own.

D= i left disconnected from the module

PIC 2

I = ground from the cig lighter

E= is wire i used to tap into the + and - from the cig lighter

if you look up hardwire v1, there's a diy on which wires to tap from the cig lighter

G= + from the cig lighter going into the + trigger part of the relay (basically the part that connects the circuit or activates the wire on the relay) This is the reason why the seat control module will turn on or off based on the position II in your key ignition

J = + output from the relay that connects to the actual seat control module

H= 40amp automotive relay (can be found in any autozone, pep boys) has 4 inputs

PIC 3

K= J

L = was for the brown/red wire, but leave it disabled, you don't need it for the seat control modules to work


All the relay does is cut the line from the original + from the harness to the module when there is no power to the relay and activates it when there is power to the relay.

The seat control modules themselves are still getting power from the original oem harness. Hence the beauty of this fix, it doesn't mess around with the oem wiring too much.

I did this on the passenager side. On the driver side, you should see the same sold brown and brown/red wires. There a set of two wires separate from the other stack of wires in the front harness.

Hope this helps.

After i wrote this, raymond g posted the schematics on this other thread

https://mbworld.org/forums/showthrea...ol+seat+module

hope this helps

TemjinX2

As a update for everyone 10/18/08

i left my car idle for the past 6 days while away on a business trip with the seat module plugged in using my relay fix.

The car still runs, with no battery drain issue and so does the seat module.

I will eventually move onto the driver side. i've just been lazy since i never move my driver seat anyways.

c32jet

Great info - Thx. Will give this a go.

1qikctr

nice write up !!! you are freakin good with electronics !!! keep up the good work mike !!!