I have a mitsibishi 2004 endeavor. That hatch keeps opening by itself and I can't keep it locked. At first I couldn't open it from the outside and now it just pops open while driving.

SOURCE: lift gate does not work in 2004 mit endeavor

This is due to the microswitch inside the glass hatch failing. It will not let you open the door because it is unsure if the glass is open or not.

Here is how to verify this:

Manually open the glass hatch.
Remove the two philips screws from the cover on the back of the handle area, and unscrew the plastic plug with the slot in it.
You should now be able to remove the cover.
You will see the harness coming off the glass handle going to a connector. Unplug this white two wire connector.
Your rear hatch should now open normally, just without glass opening.

To repair this, you will need to replace the glass hatch handle. It is a dealer-only part, and the cost is about $35.

To replace it, simply remove the 2 10mm nuts behind it (visible with the cover off that you just removed) and replace the handle and plug it back in.
Now all functions will work.

If you have any questions, just ask :)
If this has been helpful please be sure to rate me :)

SOURCE: rear hatch does not lock

You need to take the trim panel off the rear hatch,look inside ,see if the linkage is off on the key tumbler,but it sounds like you need a new tumbler. With the trim panel off take the tumbler out.A GM dealer will have the tumbler but it will come with a different key.

SOURCE: Power Door Locks - 1996 Honda Accord Wagon - Rear Hatch

I used a utility knife to create my own access panel in the plastic. Get huddled in the back interior with a utility knife and make a rectangular hole plenty big to get your hands through in the center and just up from the bottom a couple inches (just above the actual latch). Once you have visual access, you can watch the mechanism work and see where along the linkage your problem is. Mine was a broken plastic clip that was supposed to hold the 'L' end of metal arm into a hole. The arm was floating loose, and I re-secured it into the hole using some wire. You'll have duct tape decor (and an access panel where Honda should have put one in the first place) and hopefully a working hatch to show for it all when you're done.