If you turn on the drivers side it will stay on for about 15 seconds. if you turn on the pass side also the same thing happens. Although if you turn on the pass side only it stays on and seems to work ok

GMC had a bullitin about this problem. The #03-08-50-003 bullitin reads:

Seat Heater and/or Memory Power Seat Inoperative (Replace Memory Seat Control Module) - (Jan 21, 2003)
The subject is : Seat Heater and/or Memory Power Seat Inoperative (Replace Memory Seat Control Module.

The Cause is:
A logic lockup of the memory seat control module may cause this condition.

You'll need a Tech 2 connected to the vehicle and monitor the parameters in the sensor data list for the driver seat module. I doubt you have this tool, I know I don't.

But....you can try turning your car on and let it run. Then plug in the seatbelt on your passenger side (the seatbelt has to be plugged in for the seat heater to work). Then listen under your seat and activate the seat heater switch between off and on. You should hear the relay switch clicking. It's pretty easy to hear.

Now go to your drivers side and do the same. See if you can hear the click. That click between off and on is good.

Other than finding a defective relay in the circuit, trouble shooting is beyond the average persons ability without a Tech 2. GMC had a bullitin about this problem. The #03-08-50-003 bullitin reads:
Seat Heater and/or Memory Power Seat Inoperative (Replace Memory Seat Control Module) - (Jan 21, 2003)
The subject is : Seat Heater and/or Memory Power Seat Inoperative (Replace Memory Seat Control Module.
The Cause is:
A logic lockup of the memory seat control module may cause this condition.
You'll need a Tech 2 connected to the vehicle and monitor the parameters in the sensor data list for the driver seat module. I doubt you have this tool, I know I don't.
But....you can try turning your car on and let it run. Then plug in the seatbelt on your passenger side (the seatbelt has to be plugged in for the seat heater to work). Then listen under your seat and activate the seat heater switch between off and on. You should hear the relay switch clicking. It's pretty easy to hear.

Now go to your drivers side and do the same. See if you can hear the click. That click between off and on is good.
Other than finding a defective relay in the circuit, trouble shooting is beyond the average persons ability without a Tech 2.