I have a mazda 3 2005 the trunk relese will not work the key will open the trunk

Hi,

Please check attempt to open the trunk with the key and with the normal trunk button (in your car) to see if the trunk will open and then check within the lid to see if there's anything that would affect the lock when you close the trunk. Thank you.

You did not indicate if the key turns or not ... but regardless ... it sounds like you have a trunk latch mechanism issue and not a key lock issue ... and your remote cable from the passenger compartment to the trunk is probably broken. Not a good situation.
I am not familiar with the back seat of that car year/model ... but I would try to remove the bottom part of the rear seat to then see if there is a way to remove the top section of the seat. What you are trying to do is gain access to the trunk from the back seat ... since it sounds like your mechanism is jammed.
A low odds of success could be to take some pressure off the mechanism by pushing down on the trunk lid and then trying the key .. probably will not work but it is easy to try

Push the trunk releses button inside the vehicle .

Check where the wiring harness runs up the drivers side trunk lid support arm. I just fixed that exact same problem on my Caprice. The ground wire is probably broken. When that happens, there is enough to pull the soleniod when there is no load, but when the trunk is closed and there is a load on the latch, there isn't enough power to pull the soleniod open to release the trunk. Is your license plate light working? They use the same ground. -------------------------------------------------------
Launch X431 Master

is the key turning in the trunk lid?

there is a little finger in the latch that closes when the trunk is closed chances are that the little finger has closed but the trunk is still open... this can be fixed by looking at the latch on the lid you will see a slot with a metal arm in the middle take a screw driver and place it in the hole in the slot at the top. press the button on the fob to open the trunk while your pulling down on the screw driver the little latch should twist letting the screw driver move through the track and pop out now alowing you to close the trunk and being happy again.

Assuming the car battery is ok (if not, buy a male to male cigarette lighter at the auto store and connect to another car until charged enough to unlock the doors...but don't try to crank the ignition!). The trunks won't open if the battery went dead with the alarm set because arming the alarm physically locks the releases.

Sounds like the key code is switched off because you replaced the key fob battery. Try unlocking the car manual with the key in the door lock. Then switch the ignition on to reactive the keyless entry. If this does not work, you might also try pressing the fob unlock button with the key in the door lock until the dash led flashes.

find the trunk relese wires in the loom going to rear find the correct colers from your wireing diagram cut them, pear the wires going to trunk...simpely trip the lock with a 12 volt alarm battery or somthing like that any thing that can give it 12v O.K.?

is it locked from the out side some models you can lock form out side with the key try to open your trunk with your key then use your relese

if it can be opened from the outside i guess yo dont need t lock it in the first place right?!! wel that's a joke ok

now if you can drop the back rest of the rea seat you ca crawl into the trunk and pull the lever to relese the trunk open hopefully there is not much of stuff inside our trunk!!!!