I just fixed my seat on the GXP. I had a broken wire AND a bad module.
Look here: http://www.gmforum.com/t281121/
It'* most likely the pads. Start by finding the module, unplg the small plug and check the resistance of the pads. The pads are in series, so no resistance means a broken wire or bad pad.
You can compare the resistance to the Good passenger side.
If resistance seems to be OK, swap the modules.
I would suggest taking the module off the BAD seat and put it on the Good seat.
If the Good seat still works, the module is OK. The modules can be swapped without pulling the seats.