If the other key works fine then it's not your GM3 module.

The rechargeable battery in your key is most likely all that's worn out there.

It's not as simple as replacing one in the typical remote style, as it's soldered into place, and taking the key FOB apart needs to be done correctly and carefully or it can be damaged to where it's more expensive to fix, or completely ruined, but if your other key works and that one is fudged, the battery in it is where I'd start, and Scott can take care of that also.