I had a similiar problem on my 99 LHS. I've read a lot of stuff saying that most people have replaced the seat or choose not to repair it at all due to $$$. For those willing to put in the time, my seat was easily repaired. I discovered by using a multi-meter and wiring diagrams from Auto zone, I discovered the heating elements in the seat cushion had no resistance there are 2 elements (heating wire) in the seat bottom.
1. Unplug the connectors that come to the floor to the seat.
2. Remove the seat completely from the car.
3. Unbolt the 2 links that recline the seat back.
4. Unbolt the seat back from the seat cushion.
5. Remove screws from the trim that holds the seat controls and pull away from the seat.
6. Disconnect the Green connector with 2 wires under the seat, this is the heating element connection for the back.
7. Lift the back off of the seat.
8. Pull away the seat cover at the base, it comes off easily with your fingers.
9. Carefully lift the seat cover off the foam, only the outer edge of the cover can be pulled back at this time.
10. Using a regular screw driver, place the blade into the "hog rings" and twist. The rings are kind of like a key ring an rotate off easily. There are about 6 and this will allow the remainder of the seat cushion to be pulled back.
11. You will now see about 6 wires soldered to smaller wires glued down to the foam at the rear of the seat. Repair any broken wires and resolder, glue back into place.
12. Follow the other wires going to the front of the seat, this is the element around the back of your knees. Remove the white tape covering the soldered connectors. Using a Multi-Meter, check for any resistance, if none this one is broke also. If the solder connections were o.k., you have a break in the wire somewhere. The heating wire is sandwiched between the foam, you'll will need to pull the foam apart to see the wire. Mine was easily discovered, a small burn mark showed up on the foam where the wire was broke, the insulation was still covering the wire. I Gently pulled the wire and the insulation stretched apart because the wire was broken within. I stripped the wire and resoldered.
This was a repair I thought would be more techincal like the heating module, BCM, or broken ground that I would never find.
This seat is now HOTTTT!
The time spent checking wires using a meter is the way to go. My passanger seat worked fine so by comparing the readings from one seat to the other, It was easy to find the root of the problem.