How to fix the rear hatch lock on a 1996 Dodge Caravan
I had the same problem and fixed it using the following steps. I am not an expert or even very mechanically inclined, just desperate to get this fixed without spending any money. This was done on a 1996 Dodge Caravan. Similar steps should apply to a number of years of the Caravans and Voyagers.
Two people will make removing the panel easier. To do this, you'll need a phillips screwdriver, penetrating lubricant, and pliers.
First, if you cannot open the door at all: There is a small plastic disc plugging a hole just above the latch on the inside. Pop out that disk, and use a screwdriver to lift the latch mechanism. It should not take a great deal of force to move the latch. When the latch moves, push the door and it should open.
1. Remove the plastic panel on the inside of the van. You need to remove the handle and several screws on the perimeter of the door.
2. Disconnect the interior door lights by gently pulling the wiring harness (two of these).
3. Looking at the door from the interior, there is a small electronic plunger mechanism on the right side with an "accordion" (this is the electric lock). There is a rod that goes from the to the middle of the door, just above the lock mechanism. Another rod goes from the key lock to the latch. This rod, threaded on one end, snaps into a small bracket on the latch. It may need to be snapped back in. There may also be a rubbery/tar-like sticker near the locking mechanisms that can be removed (it can interfere with some of the moving parts).
4. Manually operate the plunger on the electric lock several times using pliers. Mine was extremely stiff. It should move the rod at least a full inch.
5. Spray lubricant on the latch, the back of the key lock, and the back of the exterior handle. Also spray lubricant into the key lock itself (where the key goes). Do NOT spray lubricant on the electronic lock mechanism or plunger.
6. Just above the latch, there is a small hole (only about 1/8" around). Carefully and liberally spray lubricant into that hole in every direction (this is where the rods from the key lock, electric lock, and latch meet). There is a white plastic post that comes out through another nearby hole. Spray lubricant liberally into that hole, too.
7. Again, manually operate the plunger on the electric lock several times using pliers. It should be considerably smoother to operate.
8. Put your key into the key lock and pull it out several times.
9. Spray lubricant into the key lock again, then carefully operate the lock with the key. If it didn't work or was stiff before, it should operate much more smoothly. Operate the electric locks several times.
10. When operating the lock, you should see the plunger on the electric lock move to its extents (at least an inch). Watch it when using a key and using the electric lock.
11. Check the movements of the rod and plunger when operating the lock, and the movements of the latch when operating the handle (when unlocked). If anything is still really stiff, use some more lubricant and operate the lock and handle again.
12. When reassembling the door panel, remember to plug in the two wiring harnesses for the interior lights.
I hope this helps!