Sounds like you may have corrosion on one or more of the ground buses, I tried finding a diagram to where they are, I think there are 2 or 3 total.
One or two should be under the driver side panel that is below the door by your left foot, you may have one at that module, I'm not sure though.
It is a metal bar with teeth that go into a wiring harness to distribute the ground.
The corrosion could just bee with the wiring going to that module, hopefully it is and it is a easy fix for you.
Do you have a multimeter?
2006 Pontiac Grand Prix GT with SC
1996 Buick Park Ave NA