If you are not familiar with how to take off the door panel YouTube videos often help. "how to remove door panel on a 1999 Chevrolet truck" or something similar.
The bad thing is the door is shut, this will make it difficult to remove the panel without maybe damaging it, getting to the fasteners may prove to be a challenge.
A small time body shop might do this rather quickly and inexpensively they will know what needs to be done, once inside.
However, should you want to try a last ditch effort before taking it somewhere try this.
Other than taking the door panel off inside and actuating the mechanism by hand then repairing whatever is wrong inside.
I have found this to work on stuck doors.
Try to the best of your ability, "unlock the door" (as if it would open). I mean make sure the lock mechanism is in the off position (inside) you might even do it with the key from the outside, just make sure it's unlocked, to the best of your knowledge.
Have someone hold the outside handle open even roll the window down and have them hold the handle inside (open) your second try.
Lay something like a small piece of plywood on the door panel even a towel folded up to sort of cushion the plywood, flat as you can get it, as close to the rear of the door as possible. This will spread out the "load", maybe prevent damage to the door panel (like busted plastic).
Lay down in the seat and give the plywood a good swift mule kick.
Hopefully it will pop open.
I have done this on different cars for friends and family, even in the auto salvage yard when a door needed to be opened
Should it come open during your kicks inspect the situation maybe a chunk of wood or a toy got slammed in there, thus wedging it tight. Could be that you need to spray some lubricant in the mechanism in the jamb just do this prior to closing it back.
I also looked in YouTube for your exact situation you may find something similar for other cars, if you alter search wording.
Let us know how it goes.
(never had that problem with mine)
Tuesday, May 30th, 2017 AT 1:06 PM