Seat Heaters

(Igor Kessel)
This info from the wiring harness in an '89 200TQ, the Coupe/90q 20V may be different:

For LF:
Two connectors to the heating element: BLK/YEL to BRN/BLU = 1ohm
Two connectors to the thermister that controls the preset: BLK/WHT to BRN/BLK = 8.2k cold

For RF:
Two connectors to the heating element: BLK/RED(x2) to BRN/BLU = 1ohm
Two connectors to the thermister that controls the preset: BLK/GRN to BRN/WHT = 8.2k cold

Some people have successfully repaired bad heating elements with solder and shrinkwrap or crimped connections at the burned out area, but you might want to just replace the whole element with a new one (as described below) if you don't feel confident with this type of repair.

(Phil Payne)
The usual reason is a broken wire in the seat element. The elements are wired in series, with a sensor in the seat element.

  1. Remove the seat and separate the seat and backrest. The plastic trims that cover the hinges are secured by plastic plugs that are pushed in flush with the trims. Push them out from behind and the trim comes off, revealing the clips that hold back and seat together. You have to take the connector to pieces, among other things. Note down carefully where the wires go.
  2. Remove the seat covers. You'll need pretty strong side cutters to deal with the 'hog rings' that secure the cover to the steel wires passed through the cushions. More of this later. Clear out all the fragments.
  3. The replacement element (P/N 4A0 963 555 for the seat) goes inside the cover. Lay the cover face down on a flat surface and lay the replacement element on top. Note that the wires should come towards you - not towards the seat cover surface. Otherwise you'll feel the lump when sitting on the seat. You can see that you'll have to cut two slits with a very sharp knife in the cloth backing of the seat cover to thread each arm of the element through - it comes out the other end and the tab is folded over. You actually cut through the cloth backing and the thin foam layer - the element slides in right behind the old element, which stays in place. Don't even think about removing it. When you replace the seat element (as opposed to the backrest element) you still need the sensor in the old element. Cut the slits at 45 degrees - otherwise you'll get a small ridge in the seat when reassembled.
  4. You need two tools for stretching the seat cover back on. You can use cable ties, but the official way is much better.
    1. The Hook. You find these in blister packs for picking seals (such as brake piston seals) out of their hidey holes. Most such packs   have at least one strong hook with a plastic handle - sometimes they're double-ended. Or you can make your own out of coat-hanger wire.
    2. The "Hog Ring Pliers." Examples include Mark-Line 12108 pliers, Snap-On YA808 (not as expensive as most Snap-On stuff), and Eastwood 52019 or 52032. You can probably get a similar tool at an auto upholstery shop.
  5. You also need a pack of hog rings--Audi's cheapest spare part. N 015 261 1 is around $13 for a pack of 100, or usually available from the same source as the pliers.
  6. Put the cushion on the frame, and start stretching the cover over it. Remember where you cut off the old hog rings? The replacement procedure is to load a ring into the pliers and hook the top of the 'C' shape into the seat cover wire. Then get the hook and pick up the wire embedded in the cushion. Then LUNGE - pull the seat wire up, at the same time as pushing down with the pliers, and hook the seat wire into the bottom of the hog ring 'C'. Then, with a smirk, just squeeze the pliers shut. Takes seconds with practice, and produces a really tight seat. Pay especially close attention to how the extreme rear of the seat feels when you sit on it, before you nail everything down. Remember the fairytale about the princess and the pea?

See also: Leather Care, Seat Heater Switch Bulbs

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