Fortuner back door is jammed shut

You didn't say what year or sub model

Will be either a door lock motor assembly (the four doors); which has door switch built in, grounds the purple & white wire, or the hood switch, or the tail gate switch. You can test for the grounds or disconnect the following to test by area:

Connector C0428 on the CCU - pin 21 (the four doors), pin 22 (hood), pin 23 (tail door). Automotive door switch are normally open when door is closed and close or short to ground when door is open.

I would test the hood and tail gate first

bad earth or faulty open close switch in one of the doors
start at the tail gate and work forward

obviously a problem with the auto mechanism , is there a sensor located , see your owners manual, in a particular area that has to bee kept clear and you may have inadvertantly placed something over the sensor , just guess as something must be telling the tailgate to shut , with the age of vehicle is it still covered under makers warrenty ? i'll look into the sensor thing

try open the left back door first then the outher one

My 98 has this sometimes... The only thing I do is use a screwdriver & Flip the lever till it is all the way open again... As for the plastic, Mine has broken almost every screw mount hole but still really cant get to it easily...M... (EVIL ZJ)

you may have a bad switch which is located on the latch asm

more likely than not the latch has closed some how if you have some one hold the the handle to open the tailgate you can open the latch by hand with a screw driver if your not sure what it should look like look at another door latch in the open position very simple to do and you cant hurt anything doing it this way

you can remove those bars to shut the gate BUT when you do theres nothing to hold gate from dropping all the way down to bumper. hope this helps!!!!

I would check to see if the latch is in the closed position.Using a screwdriver I would (with the gate open)have someone or your self do the action like you are opening the tail gate and try to move the striker in the door like the door is being pulled open.If the latch moves to the open positin gently try to close the door to see if it latches.

Look at the door's locking mechanism. Is the Latch Gate in the down position? Is the Door Mechanism properly tightened to the door? These are Torx/Hex head bolts. Tighten these if needed.
If the Latch Gate is down:
1. Unlock the door.
2. Lift up/out on the Door Handle as if you were opening the door.
3. Use a screwdriver to lift the Latch Gate so it lifts the Gate up and out of the way.
Alot of these Gates have plastic coverings that sometimes split and stick or cause the door mechanism to jam. Inspect the Door Mechanism for anything that could be causing it to jam. Using a pair of needle nose pliers remove any of this split plastic (if so equipped) pulling as much of it off the Latch Gate.
Use WD40 with the red spraying hose on and stick it as many openings you can and lubricate as much of the Door Mechanism as you can.
Check the operations (plural) of the Door Mechanism, Opening and Closing the Gate using the screw driver to push in the Striker Gate causing the Latch Gate to rotate back down into position. Repeat... checking for the Latch Gate to Release Up (on it's own) when you "open" the door. If it doesn't, then there is either jammed or a return spring is broken.
Have you dented or distorted the Door and / or Door Mechanism in the process of trying to slam the door close? You will have to either bend the the door area back to as close to possible the original shape. Use the other door on the other sides as a guide on this. You may have to replace the Door Mechanism itself, as when they are malfunctioning and are slammed (over and over) it could break the Mechanism itself. If the Mechanism is broke, you will have to remove and replace the entire mechanism.
Let me know if this helped, or if you have additional information of questions. Feel free to conatct me at FixYa.com!