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Discussion Starter · #1 ·
Hi

I recently successfully repaired my seated heats so I thought I'd better write up a decent guide on how to do this, as the information currently out there isn't so clear.

Hopefully this should be useful to a few of you out there, as I've heard it's a common problem, and with an independant MB specialist quoting over £1000 to supply and fit a new seat base, hopefully it will save you some money.

All it cost me was £6.99 for a set of TORX (star shaped) socket set bits from B&Q and £14.99 for a cheap soldering set from Maplin.

And a lot of patience! And some help from the 'other half' :)

This repair was done on my 2008 (UK - 2009 US) 'facelift' R171 SLK 200K. I have manual seat controls; I guess there may be some more complications for those with electric seats.

The actual problem was that the drivers heated seats lights came on for just under 5 seconds then turned off, indicating a break in the seat circuit. The passenger seat worked fine.

Now, I'd assumed that it was one of the heater pads in the seat base that had broken - not the seat back. This guide is how to fix the seat base - that's the more commonly broken part (from people kneeling on the seat for example). If the seat back is the problem area then some of this guide may be helpful, but I'm not sure how you remove the covers from the seat back - I'd guess it's more or less a similar process though - BUT - there's an airbag component in the seat back - so please be careful!!).

The repair isn't technically that difficult to do, just fiddly, and requires some time and patience. I did it gradually over a few days but I guess it could even be done in a couple of hours if you're used to doing this sort of thing.

I will break it down into sections.

SEAT REMOVAL

To remove the seat you need to disconnect the battery, to avoid issues with the airbag (SRS).

The battery cover (on a UK car it's located on the passenger side against the firewall between engine bay and the interior) is removed by twisting 3 retaining clips, one at the front and two at the back. Disconnect the negative terminal with a 10mm socket/spanner. I believe the trick is to remove it (and reattach later) as quickly as possible to avoid sparks. Make sure it's tucked out of the way safety and will not touch the battery again whilst you are working.

The advice I've heard is then to wait 30 minutes for the airbag system to fully discharge. I believe this is because if you somehow shorted

the SRS circuit the airbag could in theory fire? Not sure how you would manage to do that... I basically removed the seat and seat belt and then unattached the plugs probably only 10-15 minutes later and it was fine.

Note also that with the battery disconnected, the self adjusting windows won't operate. To avoid damage to the rubber seals, I believe the

advice is to keep the doors open when you detach the battery, and the same when you re-attach it. I did note however that with the battery disconnected I was able to safely close the door (as the window was in it's slightly down position). Don't, for example, close the doors, and then detach the battery and try and open the doors, as the windows will be in their fully raised position and you may damage the seal.

The seats are bolted down by their runners with 4 bolts. They are fancy star shaped jobs - but a standard 10mm socket worked perfectly well to remove them. You need to slide the seat all the way back to get to the front two, then all the way forward to get to the back two.



Note that MB say these are 'one use' bolts and that you should replace them with new ones after. I think this is merely for legal/liability reasons; the bolts went back in fine and nipped up nicely later. Your call on whether to replace them or not.

I couldn't find any in the UK initially after searching with a part number I'd got from here, but Inchcape said I could order them for £2.81 per bolt from Mercedes-Benz Parts, Inchcape by using part number A2029900122.

Once the four bolts are out, you can pick up and angle your seat so that you have better access to the seat belt connection.

On mine this was attached by a star shaped/TORX screw; I think it's a T45 or a T50 from other read ups? It came out easily enough and I unhooked the seat belt connection and fed it through the gap in the seat above, and unclipped the holder at the top of the seat, to free it from the seat belt completely.



You can then tilt the seat back to get access to the plugs underneath.

Just in case anyone skipped ahead, don't forget that you need the battery disconnected when unplugging the (yellow) SRS/airbag connectors!

Apparently you can unclip the black connector for the heated seat part with the battery connected, but I couldn't guarantee anything. Note that the black part of the black/white double clip that goes into the back of this (note that these two go together like a male and female, you can't remove one at a time) comes from the seat base, and the other part from the seat back, so you need to remove this too if you wanted to remove just the seat base from the car - but it's very hard to detach the rest of the connectors for the seat base that attach it to the seat frame so I'd recommend taking out the whole seat and removing the seat base when you have the seat in a more convenient position.



Note also that the seat base on the passenger side has an extra connection on the yellow SRS block and a yellow wire runs into the seat base itself. I believe this is because theres a sensor to detect whether a passenger is present and therefore whether to deploy an airbag or not on that side. In theory I guess this disconnects from the back of the yellow block - but when I tried to disconnect others from there (when I was first working out what needed to be unplugged) I couldn't remove the stubborn buggers.



Anyway, to remove the seat fully, unclip both the black and yellow connector blocks (with battery disconnected) - the black one is pretty easy, with decent sized squeezable retaining clips on the side, but the little tiny yellow tabs inside a tiny hole that need to be poked sideways on the airbag connector aren't much fun. I found the best way was to use one finger to wiggle one tab whilst pulling to release one side of the yellow block partly, then moving to the other side to do the same, and with a bit more wiggling, it should come out.

You can now remove the seat!!

They're not light - be careful not to scratch the side of the car or hurt your back. Of course, I did neither of those things :D :'(

Apparently my post is too long so breaking in half here...
 

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Discussion Starter · #2 ·
SEAT BASE REMOVAL

Once you have the seat out, it's much easier to work with. I put it on it's back on my coffee table - take care not to let the metal runners scratch the table surface (oops... oh well, we need a new coffee table anyway). Or you can turn it upside down completely and rest the seat base upside down on a desk/table.

There are two big white clips holding the base onto the frame. You pull out the tab, then prise these out - I slipped a flat head screwdriver under them to do this.



You then remove 3 screws from the black plastic side panel - these are small TORX screws.



Next is the fiddly bit - unclipping the plastic retainer tabs down the side.

You can use the other side of the seat as a guide (seat bases are interchangable); look for where the holes are to work out where the plastic clips are.

They are released by squeezing the two prongs together to make them 'slimmer' so they can then fit through the hole. There's not much space to work with though; we (I got my girlfriends help at this point - she's more dexterous than I am and has more patience) used a combination of fingers, screwdrivers, needle nose pliers, and verbal abuse. I think there was some physical abuse too - I broke at least one connector.

Particularly tricky is the double one half way down the seat. I can't see how you can get those out without breaking one.



As long as you don't break too many towards the middle/bottom of the seat base (orientation: with the seat on it's back on the table still) then it's not really a problem, as the three screws at the top hold the panel on.

Once the side panel has been moved out of the way (it doesn't come off because of the seat controls are in the way, at least on a manual seat controlled car they are, anyway - it just moves a cm or so sideways) you need to unclip the wires from the clips on the bottom of the seat base, and unclip the big black and yellow connector blocks from the seat base - there are clips on the sides.

Last bit - you need to unclip the black/white double clip that goes into the back of the black connector block. Note that these two go together like a male and female, you can't remove one at a time. The black bit goes into the seat base heater component, and the white to the seat back.

Removing this requires the patience of a saint, or brute force.

Guess which, after 15 minutes of struggling, then asking my builder/electrician (who was present, doing our kitchen) to help, but couldn't, I adopted??

:)

So... one shattered clip holder later, the plugs were out.

Even with the plug clip broken on one side, the plugs clipped back in securely. But obviously don't deliberately break it if you don't need to!



You should then be able to lift the seat base off the car!


SEAT BASE COVER REMOVAL

Removing the leather cover from the seat base was suprisingly easy - with the help of this guide here:

http://www.slkworld.com/slk-r171-class-diy/24884-diy-r171-seat-heater-repair.html

Basically, you just have to tug out the plastic trim that's sewn into the end of the leather, and tucked into a thin channel all around the seat base, from one end, and work your way around.



The next bit is fiddly; you have to unclip some metal poles from white clips - you need three hands to do this! Just work at it bit by bit and slowly.



It then just peels off.



HEATER ELEMENT REPAIR

Once the cover is removed, you can check the circuit with a 'beeper test'. I used a basic voltmeter/ohmmeter I have that beeps at you if you have a complete circuit.

If you plug the two ends of your 'beeper' into the black seat base plug, there should be a complete circuit, and it should beep.

Mine didn't.

There are seat heaters in the seat sides, and these unplug from the top of the seat, so I unclipped these and tested their circuits to see if the fault lied there. Inserting the beeper into both sides of each plug resulted in a solid beep, proving my side heaters were fine.

Going back to the main seat base plug I checked it with one end in one side of the plug and touching some bare metal wires on the heat pad on one side and it beeped; I switched to the other side of the plug and the other side of the circuit on the heater pads and that beeped - i.e. the wire/plug itself was fine. I then proceeded around the circuit, finding what bare metal and plugs I could to work out where the circuit ran.

The strange thing is, you can't see the circuit - I guess it's buried in the foam - but the wires disappearing into it are incredibly thin and I couldn't feel/trace them at all.



Anyway, I eventually worked out what should beep where and located the problem - one of the wires connecting to a heater pad had burned out and snapped!



I then enlisted the help of my girlfriend again - as a make up artist (free plug! Her site: Professional mobile makeup artist Nottingham :D ) she's got

steadier hands than me - AND soldering experience! So she was able to solder a wire onto the pathetically small exposed wire and connect to another exposed wire further along to complete the circuit.

The side heaters were plugged back in, and the beep tester now showed a complete circuit from the main plug!


REASSEMBLY

Putting the seat cover back on was a little fiddly, but nothing major. Reattaching the seat base was easy enough, except for those stupid clips for the side panel. I snapped another.

Everything plugged back in nicely and I put the seat back in the car. NB: don't forget to attach the seat belt before you bolt the seat down! And it's best to replug connections under the seat whilst the seat isn't bolted down either (don't reconnect the battery yet!).

Make sure the seat lines up properly in the slots; I got in a bit of a mess when they weren't - somehow I managed to slide the seat back but on one side slid the runner with it too - so the runners were out of line - that was a pain getting them back in line again!

Bolt the seats in, double check everything is plugged in well, open the car doors - attach the battery (as quickly - but smoothly - as you can to avoid sparks) - and cross your fingers :)

You are supposed to wait a while for the car 'to wake up' - the computer needs to do a few checks. I waited 5 mins before inserting the key in the ignition, then gave it a few more minutes before turning the key. The SRS light came on but went off after a few seconds - yay!

Apparently if you don't wait (or reconnect the battery with the airbag seat parts disconnected) you can end up with SRS warnings which won't go away without a visit to the dealers and a reset.

Moment of truth - turned on the heated seats - light stayed on for longer than 5 seconds... a few moments later... warm bottom!!

:D

Oh, after attaching the battery again, my windows got confused - the auto adjust dropped far too low. There's a few different guides on how to do this; think it differs between models. On mine I had to lower the windows fully. I let you of the button and pushed down once more for a second, to 'mark' the lowest point. I then held the window up button until it reached the top; then let go. The window dropped - far too low - I then had to IMMEDIATELY hold the window up button again to raise it and held it there for one second; it then dropped, the correct amount.

NB: This is my personal write up for information only, I can't accept any responsibility for anything going wrong, like airbag deployment or melted backsides! Only carry this out if you are confident with this sort of work.

Good luck!
 

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Thanks! I have stickied it! :D
 

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very nice write up

before doing this, did you look at adding an aftermarket heat element and wiring it to the stock switch?
 

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Discussion Starter · #6 ·
Thanks... I did think about it, and I'm sure I read elsewhere that in theory you can just wire it in to the existing circuit... but you'd need to make sure it's the same voltage/amperage etc and my electrician skills are somewhat limited!
 

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Thanks... I did think about it, and I'm sure I read elsewhere that in theory you can just wire it in to the existing circuit... but you'd need to make sure it's the same voltage/amperage etc and my electrician skills are somewhat limited!
I have a R172, but should the seat heater quit, I was thinking of a replacement heater element.

You did a good job writing this up.
 

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I have a R172, but should the seat heater quit, I was thinking of a replacement heater element.

You did a good job writing this up.
My driver's seat base stopped heating so I did some research on using generic replacement heating pads. It looked like the carbon fiber pads would be the way to go. Cost for two pads was about $100.

As it turned out the left side bolster pad was the defective one so I just bypassed it taking it out of the circuit and put the seat back together. Now that I have it working, the base pad and the right side bolster provide more than enough heat. I will never miss the one side bolster (probably would not miss the other side if I took it out of the circuit too) so not until the base pad goes out will I tackle trying to retrofit the generic carbon fiber pad to the base. I have read that using a generic heating pad is very doable so I'm fairly confident it is the affordable way to go.
 

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OMG...I hope this works for me.

Mine went out on me about a year ago and I have been dreading the MB repair costs that would be associated with a new seat. I have always assumed that it was something pathetically simple like that. I can't wait to dig into it and see if that is my issue. I will keep you posted.


Semper Fidelis!,
-Ivan Spencer
 

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A very good detailed description. A good help to those who might have been afraid to attempt a fix. Just one comment on soldering to fix wire. It is better to use a short length of fine copper or brass tube from a model shop or crimps from a fishing tackle shop and crimp these onto wire , as these are not affected by heat,unlike solder.
 

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Nice one, My SLK went in today for a mechanic to repair my drivers side ( heated seat light goes out after 5seconds ) however no luck , i need to sort it myself , however he said the elements where fine as far as he could see, might be controller or thermostat etc
 

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Interesting thread. Looking at the labor involved, you sure wouldn't want to pay the dealer. It'd cost a fortune. I have to laugh for the seat heaters look like no more than cheap heating pads. I wonder what they cost from MB?

Sure glad I don't have seat heaters, air scarf, electrically operated seats & steering wheel, and navigation. If it ain't there, it can't break!
 

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Thanks for your write-up. I have a 05' SLK 350 my issue is similar but slightly different. My issue is both drivers/passenger will light up for about 5 secs, flash and turn off. Neither seats work,yet the airscraf on both work..

Suggestions? I did remove the seats but uncomfortable removing the leather and not being able to put back as is..

Thanks much!
 

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Thanks for your write-up. I have a 05' SLK 350 my issue is similar but slightly different. My issue is both drivers/passenger will light up for about 5 secs, flash and turn off. Neither seats work,yet the airscraf on both work..

Suggestions? I did remove the seats but uncomfortable removing the leather and not being able to put back as is..

Thanks much!
Do you have a digital volt meter that you can use to check continuity? If so, at the back of the seat base simply pull up the material that hooks under the lip of the seat base. It comes out and goes back in fairly easily. Once it is up you will see the connectors for the three separate heating pads - one for each side and the center. Unplug the connectors so that you can test each pad individually. If the bad pad is either of the two side bolsters (or both for that matter) you can bypass them and have the center section working.
 

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Does it need a jumper to bypass or just leave unplugged?
Yes, it does need a jumper or something that accomplishes the same thing. The three heating pads are wired in series so you must keep continuity through the entire circuit. If you find one of the side heating pads is dead just cut the plug off the wires for that pad (leaving as much wire on the plug as possible) and then joint the two wires from the plug together (I just used a butt connector crimped) so the circuit is completed when the plug ends are connected.

As a confirmation that it should function once reinstalled, you can test at the main plug to see if you have continuity once you have done this repair.
 

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Disconnect battery first?

Hello, I asked this in another thread but thought if you are subscribed to this I might get a faster answer?
Sorry in advance for asking twice.

If I already have an SRS error code, should I still disconnect the battery first?
If I have the error code already and there is no power to the seat the airbags can't go off.
But if I disconnect the battery then there goes my clock, radio settings and maybe issues with the windows going up and down?

Sorry again and thanks in advance.
 
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