This is a community service message for JK owners!
If you go to shift your transfer case and it suddenly feels loose and flips back and forth with no or almost no effort, your cable may have come undone. Apparently this is a common problem, but one that somehow I have not heard about. I know it happens with older models, mine is a 2009, but I can't confirm if it affects 2012-13's.
This happened to me and it took a long time to figure out what went wrong and how to get access to the part. This is bad because depending on what gear it slipped of in, you're either not going to be able to complete the trail, or not drive home safely.
If it feels completely loose, the cable is probably disconnected at the shifter in the passenger compartment. If it still feels like there is some resistance, then it may have come loose under the Jeep by the transfer case.
You can remove the one Torx bolt on the driver's side on the center console where the shifter is and pry it up and hold it open with a small flashlight. A quick trail fix with no tools for the shifter link is to simply hold it on with your finger and shift. Some suggest you have to remove the whole center console including both transfer case and transmission shift knobs, but I had luck with it this way.
A quick fix for the undercarriage link is to hold it on with a zip tie or tape and shift it to the desired gear. This one is a lot easier with a friend that can work the shifter while you hold the cable on with your hand. Photo 1 is disconnected, photo 2 is held on at yellow part.
The OEM part number for the plastic clip is 68064273AA. There area few stronger fixes out there using metal parts if you Google this problem.
Hopefully this saves someone the stress it caused me. Please let me know if you have any questions or if I can make any part more clear.
Cheers,
Max