When you close the door because you re driving it auto locks the door.
Nissan xterra doors lock themselves.
If it does its somewhere in the door.
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The other thing that can happen is if you hit the unlock key after the doors are closed and don t open a door again with in 60 seconds the doors will lock.
Whether it is in the fob or the lock itself is what you need to figure out.
I had that exact issue a couple weeks back when i closed the passenger seatbelt in the door.
Also if you get some water into the lock switch on the door that can cause it to malfunction as well.
The car unlocks by itself if you leave the key in the ignition and you try and lock the doors.
The alarm self arms therefore after a certain amount of time leaving the truck unlocked it will lock all the doors and arm the alarm system.
Any door is opened a key is inserted into the ignition switch and the key is turned from off to on i wasn t opening the door.
All doors will lock automatically within 5 minutes unless one of the following operations is performed.
Try and lock the doors without the key in the ignition and see what happens.
If you want to change it get a new alarm if not be sure that your insurance company knows of the auto arming anti theft system and it will save you money at least with usaa insurance.
I would take the battery out of the fob lock the door with the rocker switch on the inside of the door itself then close it and see what happens.
When you open the door it auto unlocks.
If it doesnt unlock the fob is your problem.