Heated seat repair                                   

Theory of Operation

Tools/Material required

If you're at all mechanically inclined, you can do this.  And it's worth it - the heated seats are WONDERFUL!

You can work on the seats while they're in the car (which saves having to remove the plastic trim panel and the seat belt anchor), or you can remove the seat completely to a place where you can work on it comfortably and with plenty of room.  I've done it both ways; in either case, it's necessary that you completely unbolt the seats from the floor and disconnect the electrical harnesses.  The last time I did seat work, on the Aero, I just turned the seats 90 degrees so they faced out the door of the car; this was a pretty reasonable working environment.  Items highlighted in yellow are the minimum requirements - do only these steps if you want to just rotate the seats 90 degrees and not completely remove them from the car.  If you want to remove the seat and take it to a work area, do the steps in white text as well.

Remove the seat (this is for power seats) -

• Remove the T10 screw that's just below the center of the main seat control switch handle
• Working from the rear floorboard area, remove the T10 screw that secures the outer plastic trim piece to the rear of the seat (this screw faces rearward)
• Run the seat all the way forward
• Run the seat as high as it will go, front and back
• Pry out the circular plastic piece (from the top rear of the outer plastic trim piece) , then remove the T20 screw
• Pry the handles off the seat control switches, then remove the plastic trim piece 
  • Disconnect the electrical connector from the trim panel
• There is a plastic side plate that blocks access to the seatbelt bolt - slide the plate forward to gain access to the bolt 
  • the plastic plate will slide forward only when the seat is adjusted to it's highest position
• Use a T40 Torx tool or a 17mm socket or wrench to remove the bolt that secures the seatbelt to the seat
  • Be careful if you use a 17mm socket or wrench, as the bolt head is not very thick, which makes it hard to grip
• Remove the two seat-to-floorboard bolts at the rear  Picture
  • A 3/8" breaker bar will help to release the (Lock Tight-treated) bolts
    • A breaker bar is stronger than a ratchet
    • It is also compact and will fit where a ratchet won't
• Re-install the seat switch handle and run the seat all the way back
• Remove the two front seat-to-floorboard bolts  Picture

• Tilt the seat back and disconnect the two wiring harnesses at the front.
• Using an ohm meter, measure resistance from the yellow wire to the black wire on the larger plug (on the wiring  harness that goes to the seat)
• If more than a couple of ohms, the heater wire is broken, so proceed
  • (the resistance between the black and blue wires should be around 1000 ohms)
    • (this is the thermister connection)
• Tilt the seat back, then sideways, then wrestle the seat out of the car, throw it over your shoulder and take it to your work area
  • The seat weighs 50 pounds and, due to its bulk, is more difficult to carry than a child of comparable weight
    • Assuming that the child isn't struggling
      • Which is a stupid assumption, isn't it?!

       

NOTE: when you first remove the seat cover, note the exact location of the thermister (it's the thing that senses the seat temperature).  Take a picture of its location, or mark the location with a magic marker.  If you fail to get it back in the right position, it won't sense the seat temperature correctly.  This can result in the seat heater wire burning in two, or burning so thoroughly that it cannot be repaired.

All the following steps are necessary:

Two loops of stiff, heavy wire secure the front of the seat cover to a small diameter bar at the front of the seat.  Use pliers to bend the ends so these can be removed.  Picture  Throw them away and replace them later with cable ties.

There was a cable tie on the inner side toward the front on my 94 Aero; this tie wasn't on the 91.

The seat cover is held in place by wire hook loops.  They loop over a piece of stiff wire running around the inner periphery of the seat cover (the central U-shaped section, where your butt contacts the seat), then pull down and hook over the thinner wires that run across the bottom frame of the seat.  There's one at the front of the U curvature (not on the Aero seats, I think), one on each side toward the front, one on each side midway back and one at each side toward the back.  Look for silver wire pieces looping over the black cross wires.  Picture  

• There are two ways to detach the hook loop wires:
• Bend a 1/2" loop in the end of a coat hanger and slip the loop around the silver wire loop, then pull hard on the coat hanger and push up on the cross wire (use a stick to push the cross wire if it's hard to get to)  
  • Be sure that your coat hanger loop doesn't grab the cross wire
  • You'll see the head of the hanger wire hook as you pull it down; twist the coat hanger and slip the hook off the black restraining cross-wire  Picture

   

• Another way is to grab the end of the hook-wire with pliers, then pull down and twist to disengage
  • Takes a good, strong grip

   

To completely remove the cover, remove the remaining hooks/hangers, then tilt the seat forward and remove the two similar wire clips that hold the back flap to the under-wiring

• You can cut these if you want, and replace them with cable ties

On the 94 Aero there is a seat controller module that gets in the way of at least one of the hooks.  It's easy enough to swing it down out of the way.    Picture

Find and correct the problem -

Hey, you think THAT was fun?!  Now you have to find the break in the circuit!  Ari  has the tip of tips: 

• LOOK FOR BURNED SPOTS in the fabric that encapsulates the heater element wire.  

  • If you're lucky, one of these telltale signs will show you exactly where the break is

  • Here's a close-up of the damaged area on my 94 Aero Picture

To get at the connections or the heater element wiring, you will have to cut the encapsulating fabric with a utility knife, then pull the fabric aside.  The Aero heater element was buried more deeply than that on the 91.  Using an ohm meter, monitor the connection points to the heater wiring (one black wire, one yellow wire); when the circuit is good, it should only read a couple of ohms.

• Check the connections where the yellow and black wires connect to the thin black heater element wiring

If the location of the break isn't obvious, you will have to probe the heater wire at various points to see where continuity is and isn't.  I scraped the insulation back at various points using the utility knife, and checked back to one or the other connector points (black or blue wire at the connector) until I was able to isolate the break.  I covered the scraped spots with hot melt glue to protect them from further damage.  If you can think of a better way to do it, please let me know.  Frankly, I think it's risky to scrape the insulation back like this, but it's all I can think of to do when there's no obvious burned spot to indicate a break.

• Suspect points where the heater wire crosses from the inner part of the seat (the buttock area) to the outer part (the leg support area).  A pull test at these points might identify a break
  • Ari says that ALL of the breaks he has ever seen have been on the front outer edge of the seat (where the most wear occurs from getting in and out of the car)
• Once you find the break, solder it back together and cover the repair with electrical tape, or put a piece of heat shrink sleeving on before the repair and shrink it down afterward.  Ari likes the heat shrink method.  While it's tough, I worry about its flexibility.  I also cover the repair with a couple of squares of duct tape to help protect it.  Don't get carried away with tape, as it won't conduct heat.
• Connect the wiring harnesses, start the engine, turn the seat heater on and sit on the seat a few minutes to see if it heats up.  Use common sense about exhaust fumes; as in, don't sit in the idling car with the hatch door open, or in a garage, or in any situation where exhaust fumes could collect.  
  • According to the Haynes manual, it's not a good idea to let the car sit with the ignition switch in the run position but without the engine running.  
  • Be advised that seat heat will be subtle, particularly when it's not cold outside, and it may not come on at all when it's warm out.

Re-assemble the seat -

• Tack the heating element and fabric down with hot melt glue wherever necessary
  • Try to get the thermsiter back exactly where it was originally; it monitors the heat and sends control signals back to the switch/controller
    • If you don't know where it was, position it near a heater element loop
• Slip the rear seat cover flap under the seat back/bottom joint, tilt the front of  the cover up and  fit the ends of the cover wire into the tabs in the frame at the rear, then fit the cover to the seat
  • If you forget to secure the ends of the wire into the clips, or if they slip out, you can bend the clip tang out slightly so the wire rod can be slipped into position
• You can re-use the wire hook loops, or you might try long cable ties.  Picture  Cable ties work OK on the front and back positions, but it's too hard to get to the two middle positions.  All in all, the hanger/hooks work pretty well and aren't too hard to deal with once you get used to them.
• Start at the rear and furthest from you
  • Put the hanger wire/tie onto the wire frame on the cover
  • Hanger: Hook the bottom part with your coat hanger hook
  • Pull the hanger/tie down through the opening in the seat foam
  • Push up on the cross wire, pull the hook from the bottom and
    • Hanger: Hook the hanger onto a black cross wire
    • Cable tie: Secure the tie around a cross wire, cinch it up and clip off the excess
  • Repeat for each, working toward yourself, then toward the front
• Use cable ties to fasten the front seat cover wire to the subframe wire
• Use the hanger clips or cable ties to fasten the rear flap to the subframe wire

   

• Leave the plastic side trim piece off until the seatbelt anchor has been re-installed
• Connect the wiring harnesses to the floorboard connections
• Align the front mount holes, install the bolts and tighten them finger tight
• Re-attach the seat belt anchor to the seat
• Re-install the plastic side piece (the top lip slips under the side of the seat cover and wire rod)
  • Install the screw under the switch and the one at the top rear side
  • Re-install the plastic plug and the switch handles
• Install the screw that secures the trim piece to the rear of the seat
• Run the seat all the way  forward and install the rear bolts.  Tighten them firmly but don't over-tighten them and snap them off
• Run the seat back again and tighten the front mount bolts
• Check seat positioning and heater operation