The fix is at the end if you don't care about how I found it.
So, I have read the stories... "This is a dealer only fix...", "No Owner Fix Possible....", Etc.
When I got my cobalt the keyfob didn't work, the battery had died at one point and it was no longer associated with the car.
I did a butt load of research and found that there was no way to reset it like on my other chevy cars. I called the dealer and was told in fact there was no way to fix this other than going there and paying 50-60 bucks to have them reprogram it.
My car got rear ended a week later and all of the sudden the keyfob just started working.
So I suggest you just go get rear ended.............
Although this fixed my car I do not recommend you try this....
My GF drives a cobalt (hers is an 05 mine is an 06), her KF battery died recently and we couldn't get it working again.......
I hate dealer only fixes and was determined to find another option. I shouldn't have to pay them 50 bucks for 15 seconds....
So I searched and searched and searched, and eventually I found a post saying that pulling the fuse for the radio would reset the system.... No way, that's just to damn easy....
So I tried it, and it worked.. Here is what I did.
I pulled the interior fuse cover from the passenger seat.
I located and pulled the 10A fuse for the Radio (labeled RDO).
I turned the car to the on position to verify the radio was disabled.
I turned the car back off and removed the keys.
I waited 30 seconds (I'm a Network Engineer, we always wait thirty seconds after unplugging something).
I put the fuse back into the correct spot.
I then held down the lock and unlock key on the keyfob at the same time till the locks on the doors activated.
I then tested the keyfob and made sure it was locking and unlocking the doors and activating the security system.
This process did reset my security settings on her car so I had to go through the reset process (holding in the information and reset key at the same time then following the prompts).
The keyfob now works, and I didn't have to pay some ******* dealer $50 for 15 seconds.