B8 S-line front seat dissambly / repair

[gordee78]

Hi all,

Long time lurker, first time post. Benefited from various mods and fixes from this forum for years (2003 A4 Avant, and 2009 A4 Sline 3.2). Love my 2009 Sline and it has pretty reliable and low-maintenance. The one quirk is that my seat heat was too hot (even at level 1) so I knew something wasn't right. This January I finally bit the bullet to start looking at fixing this. For the life of me could not find any videos or threads to show B8 front seat disassembly or repair, so hopefully this will help someone else in the future.

This is not going to be the most detailed write up, but here are pictures for what it's worth. Most of it is common sense, but I'll do my best to mention the few tips/tricks: Time per seat, probably 6-8 hours. REALLY impressed at how these S-line leather seats are built up, but they were a pita to take apart.

My seats:

IMG_7447.jpgIMG_7443.jpg

Special tools needed:

IMG_7497.jpg

- The plastic trim tools were very useful releasing many of the one time snaps that is used to fasten the leather to the cushions / frame. Always a bad idea to use metal tools in and around leather.
- Also not shown is soldering iron, heat shrink tubing and other 'standard' tools.
- Necessary are the triple-square set, as well as torx bits.
- Necessary is a hog ring pliers and 1/2" or 3/4" hog rings for re-assembly.

The seat removal is covered in other DIY write-ups. Remove the seats by removing 4x triple square bolts. You'll need the seat powered for this. Remove bolts, and center the seat once again.

The headrest removed can make life much easier. You can remove the headrest by pushing through the leather on the "outside" pillar of the headrest. Ie driver side pillar support for the driver headrest, passenger side headrest pillar for the passenger headrest. The hidden button is about 1-2 inches below the top of the seat and will allow you to remove the headrest entirely.

It helps to have the seat at close to a 90 degree angle for easy removal out of the car, as well as working with it on a table/bench.

Then remove power by disconnecting battery underneath the spare tire well. Leave the car unpowered for 10mins to ensure all the airbag logic is powered down.

Tilt the chair back in the car to remove all the wiring harnesses located underneath the plastic coverplate. Seatbelt can be removed from the rivet by pushing the seatbelt down, and you're able to remove it through a larger hole by unlatching a retaining clip. Remove entire chair assembly out of car.

The chair has two metal pins that fit into holes through the floorpan, so set the chair on something soft on the floor. For me a polystyrene insulation sheet worked PERFECTLY to allow the pin to push through the insulation while the rest of the chair rail could sit on the surface.

As I couldn't find any write-ups on how to remove the seat back (or any manuals to tell me how to remove them) here's how *I* did it -- may not be the best way.

IMG_7454.jpg
- This step can also be done in the car, BEFORE you remove the chair and in fact this is what I did so I knew I could remove it successfully before removing chair. Also keeps chair bolted down nicely while you're seated in the backseat.
- Used plastic pry tool to move plastic snaps on the left and right side edge of the seat-cover. You can see that there are large strong L-shaped plastic hooks on the top of the seat back. And weaker, more flexible "J" shaped hooks on the bottom of the panel. Both really didn't want to budge. It was clear that the top L hooks are not meant to bend, so I tried to slide and bend the entire panel down and to the right (or left) to remove the top of the panel first, and then tilt

Here are the pics after I was able to get the panel out. Now that the panel is out, it seems like the bottom COULD be pulled out first (but you'll have to try to disengage the hooks).

IMG_7452.jpgIMG_7451.jpg

The back of the panel removed:
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The resulting chair back (upside down):
IMG_7460.jpg

[gordee78]

Now that the seat is out one can flip the seat over to find out how it is wired.

Turns out there are separate seat elements for the seat bottom and back. The seat back has a connector that is removable. The seat bottom wiring is tied very tightly to the frame, and runs directly to the wiring harness that connects the seat to the floor.
- The GREEN wiring harness below has two thicker gauge (18 or so ...) wires that power the heater elements.
- BROWN with blue stripe
- RED with white stripe
- If you follow back from the GREEN wiring harness, you'll find the two heater elements are wired in parallel. (This explains why my seat back worked, and was burning, while my seat bottom did NOT work)

If you disconnect the connector on the bottom (circled in picture below) you can measure the impedance of the seat bottom and seat back separately. My seat back read 3.7 to 4 ohms. My seat bottom read 15.7 ohms. This is where my problem was. Power can be calculated as V^2 / R, where V = 14.4 when car is running. So a seat bottom at 15.7 ohms is approximately (207.4 / 15.7) = 13.2W. Which is just not enough power to feel anything measurable. A heated blanket is something like 80-100W. I think the heater power supply is a constant current power supply, so it caused my seat back to sink all the power causing it to be too hot after a few minutes even at level 1.

IMG_7464.jpgIMG_7456 - seat back.jpg

I proceed to move the plastic pieces attached to the left and right sides of the seat. There are some plastic snaps that expand when the center plastic pin is pushed in. So to remove them insert a thin / narrow tool unto the underside to push the pin back out.

IMG_7459.jpg

On the driver side seat, there is a metal bracket that supports the plastic seat / lumbar controls. It needs to be removed as well using the 4 torx bolts.

At this point I started to disable the seat back and seat bottom individually. I would love to tell you that it was easy going from here, but it was slow and probably another 2-3 hours. Many many plastic one-way snaps were found along the way. In both the seat back and seat bottom both plastic snaps and hog rings were used to clamp the leather section (with a wire to keep shape) to another wire embedded underneath the foam. Once again I'm impressed at the build quality, but it was a pickle to disassemble. Hog rings need to be cut with some snips or heavy wire cutters. The plastic snaps can be removed using thin and stiff plastic tools. Go slow and steady and sometimes scotch helps. Controlled violence was required for the side snaps attaching the leather cover to the outside edges of the seat frame.

Here are more pics after things were dis-assembled to show you what some of those things look like:
IMG_7475.jpgIMG_7482.jpgIMG_7483.jpg

[Smac770]

The thermal sensor for overheating is in the seat bottom. Had your resistance issue been flip flopped, you would have been fine, though with a cold back.

Nice pics, though the text gives me even less motivation to repair my broken driver's heated seat circuit. :-) My break is somewhere between the green plug and the join of the two heater grids, as mine does not work at all rather than just one half working overly well.

[gordee78]

SO my particular issue was with the seat bottom.

I did remove the cover from the seat back -- but with the airbag there there were additional issues. I tried to remove the airbag, and it's hardware and was only partially successful at this. The airbag is secured at the top with a metal fin, and at the bottom with a torx bolt. But removing both still doesn't allow the mechanism to come out as the lining is sewn in there. Sorry no pics here, but the airbag is sewn into the side bolster of the seat back. And it's difficult to take it out without cutting through some of the material -- and since I didn't have any issue (I thought at the time) with the seat back, i exposed enough so that I could at least inspect and see MOST of the heat cabling.

The seat back and seat bottom can be removed from each other using these 4 triple square bolts M12's I believe (two on each side). These require Loctite when put back together.

IMG_7465_bolts.jpg
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When removing seat covers, go slow, working from outside in. Start by unlatching plastic ribs at edges of seat and seat back (not easy!). Hog rings need to be cut and removed (be careful to cut the hog rings, and not the supporting wire for the leather cover or the seat. Plastic snaps that hold ribs in the seat cover can be undone using thin plastic tool to force jaws open.

The heat cabling is essentially a single wire that gets sewn into the white fabric and it is a single wire in, and single wire out. Any breaks along that wire and you will get open circuit, or a high impedance reading on your digital multi meter (DMM). This white fabric is then glued onto the foam so it's a peach to get at. I could not see any obvious burn marks, and most of the wire is hidden underneath the white fabric.

So I started to hunt for my issue by going from the connector and identifying whether seat back or bottom was high impedance. I would say anything higher than 8 or 10ohms is an issue. I was able to follow the wire pattern in my seat bottom (in my case - which measured 15.7ohms) and at one point I was able to squish/push/pull and see that I could get an impedance change ... and sometimes get it down to 13.5ohms or so based on my manipulation at a certain part of the cushion / wire pattern. TUrns out it was at my side bolster which I constantly crush when getting in and out of my car. Makes perfect sense.

I cut through the fabric to expose the wire. It's here that I discovered the wire is actually enameled wire -- ie it copper wire that is covered in a thin (usually plastic poly coating) and so a DMM measuring the surface is NOT good enough to see if things are broken or not. I was confident enough in my suspicion to to cut through the wire here. I could then measure from the wire harness to the cut and see if I see which "side" of the wire was broken. One side would measure low (like 3-4 ohms) and of course the other side measured something like 10-15 ohms. Use this method to track down where you think breaks are -- keeping in mind that quite frankly this is complicated by the fact that you can have more than one break in a given side.

I used this method to "inspect" my seat back and found no issues, so I ended up putting it back together.

You'll also see from pics below that the single wire also crosses over from bottom of seat bottom, to the side bolster, to the extendable thigh bolster too. So those are likely places to check for issues as well.
IMG_7484.jpgIMG_7482.jpg

So what to do when you find a break? How do you solder enameled wire?

1) Need a hot iron -- I turned my weller iron up to 750-800F
2) Need to expose enough of (about 3cm minimum out of your seat), dip the end of heater wire in flux. Flux is an acid paste to prepare the metal to receive solder / tin.
3) Pool a small bit of solder onto your tip and dip the flux+heater wire into the drop of solder and it should tin the end nicely. Burning off the enameled coating in the process.

I also found that once the ends were tinned, I was able to read much lower impedance from the tinned section to say the connector. What used to read 4-5 ohms was now reading 2-3 ohms. I used some 22 gauge wire to join sections, and covered all joints in heat shrink tubing, and then cut the foam to bury the joints into the foam to protect them. I used 3M spray adhesive to repair all cuts in foam. I also used some spare pieces of felt to cover over cuts in felt, glued using the 3M spray.

After the fixes, my seat bottom measured 2.7 ohms at the green connector! Good to go!

Takes another 1.5 hours to put everything back together, including new hog rings to fasten the leather cover wire to the seat wires. (Every gap show in the seat wire below is where hog ring should be installed. Red clips are where the plastic ribs from leather cover snap into the seat. This is also a pita. Work from the center of the seat outward towards the edges.

IMG_7482.jpg

Double check that you've got the airbag back in place correctly. before installing all snaps. Put seats back together in reverse order, new hog rings and all. Pull leather so it's tight. There really is no excess here. (Approximately two dozen hog rings required per seat)

Took my first drive out this morning putting everything back together in reverse order.
- Put assembled seat in place
- re-connect all wiring harnesses
- re-connect battery
- Slide slide the seat forward and back to re-install bolts. I installed Loctite 242 (blue) into these bolts to be safe.
- Reconnect seat belt

Turned on my seat heater and even at level 3 my seat back was nice and warm (Wasn't ever able to do this in the past!). And of course I had heat in the seat bottom as well! Hope this helps!

Gordon

[gordee78]

The thermal sensor for overheating is in the seat bottom. Had your resistance issue been flip flopped, you would have been fine, though with a cold back.

Nice pics, though the text gives me even less motivation to repair my broken driver's heated seat circuit. :-) My break is somewhere between the green plug and the join of the two heater grids, as mine does not work at all rather than just one half working overly well.

So if this is the case, all that wire is exposed on the underbelly of the seat. The real pickle here is the seat cover removal. If you think it's between the green harness and connection to the seat back / bottom -- you can follow the two wires (BROWN with blue strip, RED with white stripe) about 12-16 inches back and you'll see where both wires have a heatshrink -- this is where both the back and bottom are connected to the harness. Circled below:

Capture.jpg

You may have a bad crimp at the wire harness, or a bad union under the heatshrink. Either way this may be easier test (than chasing down bad heater wire).

[Smac770]

Ah, cool. I'll have to look into that; thanks.