Only leather seats are offered with heat. Interesting though. Though I almost never need them here, mine (in my '07) warm up quickly, heat almost too much on low and I can't use high, too hot. I wouldn't think the leather is the issue, though. Sounds more like possible bad relays. The relays are under the seats, and located together, but they plug in like any other relay. On mine, the high temp relay is a 4-pin, and on low a 5-pin. Relays are tested for continuity between pins 1 and 2 with power and ground to 3 and 4 or 5. It might be worth checking them. The systems are simple, though - all you have is the switches, the relays, and the elements.