The trunk gets to the point of closing, but it does not latch shut. There don't appear to be any obstructions. The latching mechanism seems closed and won't "unlock."

Spray some white grease on the latch mechanism, both sides.

Then, with the hatch at 3/4 closed, insert a phillips screwdriver through the latch hole, pull down, and pull on the release handle.

If that doesn't work, you will have to remove the inside panel. Take off the plastic handle surround on the inside, remove the 'top' portion first and then pull the plastic up and out. You will probably break a clip or two from the bottom, the plastic clips pull straight out and away from the door. Then lift the panel up and off, the top clips should slide out of the holders.

There is a metal rod that moves the lock. Search for it on the passenger side(?) and pull it to get the lock to release. You will probably find a broken plastic rod holder, which cannot be repaired.

Klaus

I have a wagon and have solved different issues with the back door including a broken handle. It seems your door lock is locked preventing from closing.. Check the electrical connection and make sure it is operating. It can be tricky. mine was not working for a while and out of the blue started working. if you go into the door mechanism and find a loose rod I devised a simple fix it for the problem of broken plastic connectors. I have solved it joining the rod to its location with one or two short zip ties on each end through the metal hole that used to house the plastic connector. They work better than the original to solve this problem which happens often on the driver's door on 850's with high use .