Check both upper and lower element circuits, unplugged with an ohm mater to determine which one has a broken wire, IF that's the problem. Make sure there's 12 volts going to the elements first. It's usually only one of the two elements per side, usually the lower one. It's also not exactly a "fun" job. It can be done in the car with the seat unbolted but it's easier if the seat is removed from the car. Be carefull not to bump the SIPS bag actuator when (if) removing the seat.