I had the same problem with mt 2001 grand cherokee, just fixed it yesterday. The problem was that the lock was stuck in the locked position.
pull off the inside door panel by removing 2 screws, one by the door handle and one in the arm rest. and then coax it off. there are about 5 christmas tree attachments that also hold it on. undo the electric connector and the push/pull rods for the door lock and door latch. peel back the sound insulator from the rear edge of the door so that you can see the big opening and a couple of other holes in the door inner. now you can peek in and see the works of the latching mechanism. I just broke of the plastic cover tats over the mechanism. its just for anti theft. not sure if you need to do this or not. Now spray the crap out of every thing that you can reach with WD40, you will need to use the straw thing on the WD40 so that you can reach everything.work from the large opening in the door inner and also from the small hole that you see behind that opening so that you get everything sprayed well.
now you need to reconnect the electric connector so that the lelctric door lock and window will work but leave the door panel off. roll down the rear window and open the front door. Now pull and push on the door lock push/pull rod and lock and unlock the electric door lock switch on the front door at the same time. Just keep dooing this and eventualy you will hear the click of the door unlocking. then the door will open, but the jobs not done yet. now that the doors open spray the crap out of the door latch in the rear of the door and also in the hole under the latch.(you may as well do this step to all of your doors, and repeat every few months to avoid the problem in the future. Now get a small screw driver that will fit in the hole and as you pull and release the outside door handle help the mechanism go up and down thru that hole with the screw driver. now give everything another good spray with the WD40 and keep working the door handle and also reach inside the door and with your hand help the mechanism move as far as you can move it. You will feel everything start to move more freely. you should be all set now and can put your door panel back on. open and shut the door a few times but leave it open for a while when youre done and any access WD40 will drain out the bottom of the door. one last step, spray the manual door lock buttons with WD40 so that those move freely, I noticed that mine werent always locking or unlocking when using the electric locks, and this seemed to solve that problem.
Hope this works for you. It did for me! Enjoy your working door.
