I'm having the same problem and i know for sure it's not a blown fuse because sometimes it works and sometimes it dont. Its probably a short in some wiring. The dealer said it will probably run me $250. Can you say head-crack?

 

Bringing a thread back from the dead... But now im having the same problem....

Weird my key fob works but... when I press the back button on the trunk and the button inside the cabin it does not work.

I have a 2007 so still under warranty.. sigh I tried some of the things in here but I figure if it dont work ill take the 2 hour drive and head toward my wretched dealer...

 

This is a really old thread that I only found on a google search. I wanted to share that I had many of the same problems posted here but diagnosed and fixed my problems:
Problems:
Trunk release on dash did not work
Exterior trunk release button did NOT work

The only way for me to open my trunk was with the key fob.

As usual start with the most simple obvious causes first:

Problems:
The dash button did not work because the switch in the inside left of the lower glove box was switched to off position. Switched it on and the dash button worked. Trunk button still did not work

I fixed the trunk problem after I daignosed the problem. The casue was that the wires to the exterior trunk relase switch on the rear of the car had come completly disconnected from the weathpak connector which gave them power. I found them hanging loose in the bumper cover reconnected them to the plug, soldered and all works just fine! Here is how I did it:

Remover the dirver side tail light assembly by removing the interior trunk panels, removing 4 8mm bolts which secure it to the body. Once removed a 10mm bold head will be seen which connects the bumper cover to the body of the car. Remove this so that you can pull the bumper cover away from the car for access to the switch and wires. There is a blue weather pac connector. The female side of the plug has 2 wires (black red stripe and black green stripe). The maile side of the connector has 2 white wires which go to the exteriro trunk switch. I found that the whilte wires has separated fromt he male side of the connector. I verified that the switch worked by testing the bare ends of the white wires with a multi meter. I I then shaved some of the plastic off of the connector until the metal crimps inside the plug were visable. I stripped 3/4 of an inch of insulation off of each white wire. I folded them until they were bulky enough to be crimped in the exposed points inside the male end of the plug. I soldered them there for good measure and sealed with black electrical tape. I rerouted the wires. Plugged it in and tested it. NOTE: in order for the button on the exterior of the car to release the trunk. . . the lid MUST be CLOSED PLUS you must have the intelligent key with you! I reassembled it and tested again. All is in perfect working order.

Now I have all trunk funcitons. . .interior dash release, exterior button release with key and my remote works. This was an important fix for me because I use my car for work and need to be in my trunk 5-10 times a day!

Hope this helps somebody out! If I can help, send me an email if I can help!

 

Im not sure if you are aware of it or not but I haven’t heard you mention all possible locations for the 3 fuse boxes ..,did you check all 3...? Ok the Trunk switch may possibly be in one of the two fuse boxes usually located near the battery... the one you want to start with is the one tucked away back on the firewall... then the more visible one... then the fuse box on the driver side floor panel on the left....good luck