Here's the problem: Whenever I open the trunk with the key when all the doors locked now, the alarm will sound.

Since I have a GXE, I can use the keypad to unlock the trunk from outside the car, but would still like to get this fixed. Anybody have any ideas?

 

I think the problem is that the alarm isn't receiving the ground signal (which says "disarm"), either because the lock cylinder for the trunk isn't sending it (dirty contacts, worn out switch, etc) or there's a break in the wiring between the alarm and lock cylinder. Probably the lock cylinder. I'm just learning more about this system too for my keyless entry, and whooo boy those cylinders do a lot more than just sense locked and unlocked!

Again, I'm not 100% sure this is the problem, but hopefully this will get the ball rolling. Good luck.