Theory of Operation

Tools/Material required

Quick check: With the ignition switch in the Run position, you should be able to hear the seat heater switch assembly make a kind if click or "ching!" nose when you switch it; that's a relay energizing.  It may do it at each switch position or at only one position, but if it does it at all, then the problem is most likely in the seat heater element wire itself.  Although I have had a switch fail, seat heater problems are almost always in the seat heater element. 

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 seat cover -

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  

Try removing the front 2 or 3 hook loops, then lift the front of the seat cover and see if you can see a burned place that indicates the problem area.  If so, you probably won't have to remove the rest of the seat cover .  Picture

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

Slip the front of the cover up off the seat bottom, then tilt it up.  The outer wire frame of the cover hooks into clips at the back of the metal seat frame;  tilt the cover up and slide it forward to release it

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: 

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.

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.


Re-assemble the seat -

Re-mount the seat -