I have read lots of threads but there is no a lot of info, I presume these people just went to the dealer in the end or lived with it broken. I am keen to try and fix this myself if someone is kind enough to please guide me.

From what I understand there is small chance the wiring is disrupted and a much greater chance the heating element is broken. The heating element requires $$$ from the dealer otherwise some people order it and get a upholsterer to install it. Dealer is not an option for me unfortunately.

There are a lot of wires under there! Any way to confirm the cause?

Front


Back


Close up of back

 

did you check the fuse?

 

Sounds stupid but I couldn't actually find a description of where to look. Is it in the engine bay or is there a panel inside also?

 

not stupid at all bro, i actually looked and could not find it either

umm, does the button light up when you press it? if not it might be the button itself.

 

The button stopped lighting up, both the one and two settings. The drivers side works perfectly, just the passenger stopped working. I did find one post where someone said that there isn't actually a fuse for it but that sounds strange.

 

I had the same issue with mine. 2 wires were torn under the seat. Individually check each wire under the seat and make sure everything is secure. If everything is secure, you have to use an ohm reader and check if there is an open circuit for the heater element. Most probably you have torn wires under your seat, its tight under there and they'll be hiding from you. Good Luck!

 

Check fuses 25 & 41.

If OK check wiring & heater pad.

As no lights are showing I suspect a fuse.

 

Thank you for the advice, I will do this over the next couple of days.
Thanks Glyn, I found the fuse box, they both looks perfectly normal to me so onto the next step. I will unbolt the seat this weekend to look underneath. The lights are still working for the drivers seat.

For anyone else the fuse box is on the side of the dash under the plastic panel. It is the drivers side no matter if your car is right or left hand drive.

 

Good luck with it. Before you go to the dealer check ebay or junk yard for replacement seats, might be cheaper

 

So I pulled the seat out of the car. Everything looks in pretty good condition. Most of these wires I suspect are to do with the seat adjustments. Can anyone please tell me which ones might be for the seat elements?



The large brown and red wires I assume are the main 12+ and ground but I suspect they are used for everything and not just the seat heaters?



These appear to be the only wires going into the bottom of the seat, one is a vacuum tube so one of the other two must be the pressure sensor? and maybe the seat heater?



I can see how some parts are very tight, especially here around the hinge joint. nickp- did you pull the entire seat to pieces to find the culprit? or were the wires somewhat accessible?

 

Yay fixed! The light is on!



I ended up removing the seat entirely, taking the bottom off and finding the loose wire. If anyone needs to do the same this is how. Remove the wire plugs from the two plastic boxes. Take the vacuum hose out (takes quite a lot of force but luckily did not break). Then the next step is to take the bottom of the seat off. First take these 4 black pegs out of the clear plastic thing. They pull out easily with needle nose pliers.



Then simply remove the clips, they need to be carefully levered up with a flat head screwdriver.



Then you simply push these long rubber things to the side to allow them to pass through the spring and spring perch.



The vacuum adjustment knobs were a pain in the ***. This is what it looks like when removed. You simply (retrospectively anyway) unhook the small white clips at both ends and the black plastic cover and the switches come upwards.



Then you are left with this that you can unscrew with a 10mm spanner.



The heater wires are the large brown and blue ones. I did not realise but someone had already attempted a repair on mine, see the pink shrink wrap in the picture coming out of the plug. This is what my problem turned out to be.





So I cut the blue wire and soldered in a new piece with a connector in it.







Hope that helps someone. Also I read somewhere not to even put the key fob in the ignition while the wires are disconnected under the seat, it will trigger an ABS error that the dealer needs to reset.

 

Nice job!

 

Round 2! Now the other heated seat is not working. Fuses 25 and 41 are fine. The wiring is fine this time. Testing the other seat, the resistance through the heater panels is 0.2 ohms.

Both seat cushings run in series, ie 12V+ to seat bottom, gnd- from seat bottom to +ve seat upright and then back to car gnd-. So if you split the wires then you can measure each one. Together there is a short but the upright is fine so it is a shorted seat bottom.... great.

I will tackle this one in the next month or so, perhaps a long weekend and do a write up if anyone is interested.

 

Just finished the heated seat repair. Took 4 hours with mucking around. You don't have to take the seat out of the car. You can add aftermarket carbon fibre heat pads to save $1000-2000 on what the dealer charged for new ones. I ordered 4x carbon fibre replacement from ebay. They came direct from China and cost US$49 + $4 shipping. They are universal and because of the way the carbon fibre works you can cut them to size. It also means it is impossible to get a short again as there are hundreds of connections between the two latices rather than a single long copper wire.

I found the short in the seat bottom exactly where I thought it was overly hot the day before it stopped working. To get the bottom squab out just follow the instructions above, remove the 4x black plastic lugs from the two clear plastic brackets underneath. Then push the rubber long things to the side and it is now free. Pull the vacuum adjusting console off upwards by pushing on the two clips underneath. I used a mirror to help see them. Then it is just the vacuum hose and the heated seat wiring.

This link was quite helpful https://mbworld.org/forums/c32-amg-c...iy-repair.html To get the leather off simply pull it out of the clips around the sides. The entire seat is held in tightly with little while clips- very difficult to undo. They hold the leather to the seat bottom in a square shape to maintain that "bucket" look.

As we know the stock pad is sewn in place so it is fairly difficult to remove. If you do undo the stitching you then need to sew it back up again once you place a new pad inbetween. I simply placed the heat pad between the stock pad and the foam, removed the stock wiring, routed the new wire out the hole underneath and put it all back together. This is where the negative side of this approach comes in. Because the new pad sits where it does you cannot clip all these white clips in place. I managed to clip in the back and both sides but the heat pad prevents you from clipping in the middle and the front unless you make holes in it which I wasn't prepared to do. The seat has a very slight bloated look at the front which no one would notice unless they saw it before and after.

Good news is that the light is back on when I switch the seats on. Bad news is that now the back won't heat up much. The reason is because the aftermarket replacement has a much higher resistance than the stock lumbar pad, 0.7ohms vs 0.2ohms and they are wired in series.

I thought this might happen so I already put a new one in the upright of the seat also. This is a piece of cake if you do it with the bottom removed from the seat. Climb in the back, remove the two screws holding the seat backing on, pull the cover off. Now undo the bottom and side clips. You don't need to remove the leather, just slide the new heater pad up the bottom from the back of the seat.

When I can be bothered I will wire up the lumbar pad so they both heat the same and post some pictures of the whole experience. The bottom pad heats up at the same speed as the stock one did. So despite having more padding to heat through it still works well.

 

Nice find on those carbon fiber elements.

 

Did you really mean to say you saved $1,000 to $2,000 over dealer prices? Or $100 to $200?

 

I do believe he means "thousands" in savings. The dealer replaces the entire seat cover ith the heating element built in as that is how the part is shipped from MBZ. The seat bottom will be around $700 retail, the back around $800. Then add in the labor.

 

Yep as Rodney said very pricey. Its even worse than that here. You guys get much better prices in the US than most of the rest of the world. Our prices are at least as bad as Canadian dealerships.

I found the drivers seat adjustment is riveted on whereas the passenger one had bolts. So you have to pull out the vacuum hoses one by one. I labeled them and took a photo just in case.


Then pulled it all to pieces. Here is the burnt out wire. It melted a bit of the foam around it. Definitely not an easy job to solder this one back together.


Next the seat apart. The aftermarket heated seat element goes against this foam and the stock heater/leather goes on top.


This is the bottom of the stock heater. All the wires everywhere are to transfer the current between seams/sections of the leather from what I can see. I cut them all out with side cutters since they won't be doing anything useful from now on.


These clips are why my thumbs hurt. They hold the leather down around the outside of the "square" your butt sits in.


Aftermarket carbon fibre seat elements. I cut the ends off to make them fit better. Ebay link http://www.ebay.com/itm/161174766016?_trksid=p2060353.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

Test fit. It came together much better than it looks.


Remove the old wire and feed in the new one via the same hole.


I will post a photo of the seat sometime later on. Probably when I get around to wiring the lumbar aftermarket one also. In conclusion, if you have lots of money then get MB to fix this for you. If not then this is a very cheap alternative which is almost as good and you know it can never break again, not that I recommend kneeling on the seats to grab stuff out of the back seats.

 

Thanks TW2 bro. I will tackle this in the future when I feel my life needs a real challenge. Looks like quite a bit to take a part but I guess a Merc wont be complete if its features aint working.