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Okay, last night I made a second attempt at fixing my heated seats, and thought I'd post on a few tips I learned. I"ve got a 2 door 97 900 SE (leather, power seats).
Removing seats from the car was pretty easy. Move seat forward, remove rear bolts, move back, remove front bolts. Unhook connectors (2), and carry it indoors.
Heater wires for seat bottom and seat back are in series. A 2-wire connector joins them. Unhook connector and test w/ an ohmeter. The 2 wires to the seat back are easy to test w/ an ohmeter. I got 0.5 ohms, anything under infinity (broken wire) is okay. My guess is that the wire in the seat back hardly ever goes bad b/c it gets much less strain. Checking the seat bottom is a bit tricky. One wire is accessible from the connector, the other (yellow) bypasses the connector. I stuck a needle into the yellow wire and tested continuity from needle to connector. result : open circuit. There's the problem.
To remove the leather seat bottom, there are some plastic pieces to remove on the "door" side (left for non-Brit, drivers side). The first was easy. The second, which houses the power seat adjusment controls was harder. That's where I got hung up on on attempt #1. Three screws hold it in place. Screw #1 is easy w/ a torx screwdriver. Screw #2 requires a short torx bit, and has no clearance for a ratchet wrench -- I grabbed the bit from the side w/ a pair of vise grips. Screw #3 turns out to be the simplest. In the spirit of the "short belt" modification, simply twist and pull on the plastic. A distinct snapping of the plastic signals success. You now have an improved design, which requires only two screws to hold the piece in place. Your next seat heater repair will be even easier. Upon reassembly, I found that 2 screws hold this piece in place quite well, and no damage is visible from the outside. The alternative to this "modification" is a major disassembly of the power seat mechanical junk to access the screw in question.
With the plasic off, next comes the leather. From the underside, you'll see two long wide plastic strips sewn to the seat covering which are hooked to the wire mesh supporting the seat cushions. Unhook these and the loose tails can pass through the crack between the seat back and seat.
The other three sides of the seat cover are hooked under tabs on the seat frame. By compressing the seat and using just your fingers, you can unhook the seat cover (which has a stiff band around the edge) from the frame.
Looking at the seat bottom from above, you'll see a roughly square region in the middle which is still attached to the foam cushion. The way this works is that the seat covering has four heavy wires sewn into it, and the foam cushion has a square loop of heavy wire molded into it, parallel to the one in the cover. The wires in the cover and the wires in the cushion are joined together by several (8 or so ?) little wire rings (which some on this list refer to as "hog rings", i.e., to stick in a hogs nose !). These can be cut with a strong pair of dikes, or just sort of bent open w/ pliers. Try not to damage the fabric sleeves that hold the stiff wires to the seat cover.
NOTE : I removed the seat cover as described *before* looking for the broken heater wire. In my case, and maybe in most cases, the fault occurs in the high "thigh support" part of the seat (which gets flexed quite a bit as you get in and out of the car) and it might be possible to do the repair without removing the seat cover completely.
Now to find the fault. Trivial : locate the brown charred spot of foam. There is a very thin (1 mm ?) thickness of foam above the wire, but you can actually see through it and see the squiggly pattern the wire makes all over the seat cushion. I just cut through the thin layer of foam over the wire several inches on either side of the fault. Cut back & strip the wire (it's actually just stranded copper, not fancy nichrome or tungsten or "heater wire") and solder in a pice of wire to replace the bad part. Make sure it is slack. Probably no need to cover the joints, but I put electrical tape just in case.
I reassembled the seat fully before testing for continuity. Fortunately, the fix worked and I got like 1 ohm or so. Pfew.
To reattach the seat cover to the cushion (the wire part that had the hog rings) I just used some small cable ties (zip connectors, wire ties, ...). I hooked all of them under the cushion wire first, then loosely hooked them under the wire in the seat cover, then tightened them, with the tails pointing towards the outer edge of the seat. I chose not to cut them, as they're way to thin to feel or see, and there won't be any sharp edges.
The rest is pretty straightforward.
RESULT : A feeling of satisfaction at having located and repaired a significant fault. And cold buns. The friggin'. seat heater still doesn't work. Grrrrrr. Oh, and the passenger side seat doesn't even move, which means I can't remove it !
posted by 205.170....
, Thu, 3 Feb 2005 12:11:42
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