Ml320 how to manually unlock/lock the rear hatch

Yes, you should be able to use the key to unlock the rear hatch of your 2009 Equinox even if the car battery is dead. The lock cylinder for the rear hatch is likely located on the outside of the hatch itself, or it may be located on the door handle. To unlock the hatch with the key, insert the key into the lock cylinder and turn it clockwise. If the key won't turn or the hatch won't open, you may need to wiggle the key or apply more pressure to unlock the hatch. If the key won't go into the lock cylinder at all, it is possible that the lock is frozen or damaged and will need to be repaired or replaced. You may also be able to use the manual release for the rear hatch, which is usually located inside the vehicle, near the driver's side door or on the underside of the dashboard.

Searched on YouTube

Manually unlock Trailblazer lift gate hatch Trailblazer SS LS2 Envoy

Rear hatch is locked or unlocked with a key. (if equipped) • To open the rear hatch, insert the key into the lock, turn it to the unlock position and pull up the rear hatch by pressing the handle (DOOR). You can also lock/unlock the latch (but not release it) with the central door lock system. • If unlocked, the rear hatch can be opened by pressing the handle (DOOR) and pulling the hatch up. • To close the rear hatch, lower and push down the rear hatch firmly. Make sure that the rear hatch is securely latched.

The most common issue for this concern is the rear lock assembly. The lock has a electrical actuator that locks and unlocks the lock assembly. WHen the actuator goes bad, it no longer can unlock the hatch. You will have to replace the lock assembly to fix this issue. The hard part is that you have to open the hatch to do this. Most of these cars have a manual unlock but you have to find it. Look at the bottom of the interior panel on the hatch, some come with a small cover plate that can come off, inside is a lever that can unlock the hatch. Its best to have the new part from the dealership so you can see what the lever looks like. If you do not have a cover plate, then you have to try and get the trim panel off so you can reach the release lever.

Sorry, I don't have the data now..... but.Some hatches have a manual release on the inside. There might be a small plate near the door center that you can remove and open the hatch with a screwdriver.

but...I'm not sure tho about your car.

probably a leak in the air line to that door, therefore not reaching pressure.
The central locking should work on compressed air
would need to strip door panel down and check lines and listen for air leaks when operated

First, on the rear hatch, there is an actuator. On FX, when you close the trunk, it kind of **** the hatch closed all the way. When you press lock on the remote, this same actuator locks it as well.
Now,
1) when you unlock the car from the inside, go back there and press the button to open the hatch door manually, do you here any noises?
2) Close all doors, go back close to the hatch button and using the remote , lock the car and then unlock the car. you should hear a sound from the actuator locking and unlocking the lock on the rear hatch!

If you don't hear this, your actuator is inop.
Next step would be to check the fuses inside the car, on the left bottom driver side, and outside on the battery compartment.
It might be just a fuse.
If all fuses check ok, your actuator is most likely gone! Not ea expensive fix, just time consuming!

NOW, if you can hear the noises, then something is either broken inside the actuator or one of the cables is loose!
Hope that helps.
Also, what year and miles on your fx?

The lock is stuck in the "locked" position.
When you close the hatch, it is jamming the latch hook into the wrong area.

Manually open the hatch. Unlock the hatch (even tho the hatch is already open). there are two bolts holding the metal "loop", the loop has moved. Adjust the metal loop and close the hatch / lock it, etc.

the unlock or popper for the door needs to be replaced. the door should work with a key.