Driver side heated seat does not heat up when

I had the same problem with my 03 Sierra. Took it to the GM dealership and they diagnosed it as shorted-out heater elements in the seat (bottom and back). Brace yourself - they're expensive to fix. Dealer wanted just over $900 USD and wouldn't guarantee the work. Even charged me $80 to diagnose the problem. Here's some good news - the elements are available online @ www.rockauto.com at about 1/3 the price from the dealership. If you can't install them yourself (it takes some upholstery know-how), contact a local auto upholstery shop and they should be able to intall them for you for around $100-$150.

Good Luck!