This DIY explains how to repair your heated seat and/or change the cushion. It's a fairly easy job, but requires some soldering skills. You'll need XZN (triple square) bits, so don't start the job without them. You'll also be removing some plastic trim that has most likely become brittle. You can pretty much count on breaking some tabs. I broke a few, but it didn't seem to affect how the parts held on when I re-assembled everything. As with any DIY, I'm not responsible for any damage you may do to your car, yourself, or your house.
I did this repair with the seat removed. If you want to do it with the seat in place, good luck.
First disconnect your battery, negative first. You will be disconnecting an airbag connector in your seat and you don't want to set it off accidentally. Make sure you know your radio code if you don't have a setting saver device.
Next, slide the seat all the way forward. There are caps pressed into the plastic rail guards. Pop them out with the tip of a knife, remove the screws and then remove the guards.
Slide the seat all the way back. See the picture below. There are either two screws or two nuts depending on the model year. Remove the screws and then squeeze the nub between the screws and push it through the hole:
Now you should be able to slide the seat back further until the rear rollers come to the end of the track. Once there, lift them out and the n twist the seat to release the front rollers.
Tilt the seat back for easier access to the connectors. Disconnect all the connectors. I think they only go back one way, but you may want to label them. There is an xmas tree like thing that holds the harness to the seat. If you can't push it out from the back, work the other part out from the wrap and cable tie it back on when you re-assemble.
Take the seat out and lay it on it's back. Keep all cats away:
Remove the lifting handle by prying off the caps and removing the screws:
Remove the belt latch support:
Remove the knob that controls the seat back angle. It's just about impossible to remove without breaking a tab, but holds on fine with two out of three. Proper removal has something to do with popping back the black ring on the back side of the knob. Sorry, no pic.
Look on the back side of the trim where the left and right halves join. There is a well hidden clip that must be released. Once released, you can get to the screw on the other side:
Pull the trim out from the groove in the front of the seat and pull it down as you go:
Once at the edge, place your finger in the back corner of the seat and lift up on the trim to release it from the seat trim. Rotate the back up and the front down. Done carefully, you won't break anything:
Now release the connector between the upper and lower heaters. It's held to the pan by an xmas tree that is easier to get to once you raise the cushion:
Remove the connectors from the frame under the seat using a small screwdriver:
Remove the four screws holding the seat backto the bottom:
On the side of the seat, find the spot where the seat fabric begins to be attached to the seat frame. Stick your finger in there and pull down:
Once one end is out, keep working around the front of the seat until you get to the other side. (I still have my spring- HAHA!):
Once the sides and front are free, pull up on the cushion. No, it's not glued down. Your fat ass has been pushing down on it for so long, it stuck to the base.
Not sure how to explain this, but flip it upside down so that the base points one way and the cushion the other way. Lift up the cushion so that it is 270 degrees from how it normally sits. This will give you access to the back clip. It may fall out by itself, or you may need to pry the back clip open a little. Here's a picture of the back clip in the seat frame. Note the teeth that bite the trim strip on the back of the fabric:
Your cushion is now free. Peel off the fabric from the edges. The center is held on by bars sewn into the fabric. Loops at the end of the bar hook around wires molded into the cushion. You'll need to grab the bars and work the hooks off the wires. If needed, bend the hooks open a little:
Once the fabric is off, don't be shocked at what you see. Most likely the heater has seperated and is a crumpled mass at the back of the seat. An ironing board and a hot iron will fix this. Make sure it's not hot enough to melt the element. Get your meter and buzz out the connector. Remember that part of the heater circuit is the back, so either jumper the small connector or read from the small connector to the large one. You'll most likely find that you have continuity on the heater, but not on the sensor. If the heater is out, you may be able to find the break and splice it. If not, order a 3B0-963-555-C heater. It's about $135 from www.worldimpex.com.
If the sensor is bad, it's most likely from a broken solder joint. The ones that VW used are wafer type and can be tricky to solder. You may have better luck with a leaded type. One member had to buy a whole boatload of them. If he gives his permission, I'll add his username so he can send you a few (Look two posts down).
The sensor is located here. There is a reinforced area in the cloth and a lump you can feel from the back:
You'll need to dissect it out from the back. Be careful not to cut the wires. Once free, you'll be able to pull some slack through for room to work:
If you feel comfortable resoldering the thermistor, do it. Otherwise take a leaded thermistor and form it as shown:
Slide some shrink sleeve on the wires and solder the sensor in place. Here's what it looks like when done:
Tuck it back into the heater fabric by pulling the slack out of the wires. If you check continuity, it may show open. Themistors have wierd electrical characteristics. Turn the meter from autorange and eventually you find a range that shows resistance.
Now to reattach the heater. Note that it is only glued at the back, front and sides. The center floats. Leave enough slack so that the heater can go into the two slots in the cushion. You sould be able to see the old glue stains. I used Loctite spray adhesive from a fabric store, but you can probably get it at a home center too.
Now do all the assembly steps in reverse and you're good to go.