2017 Mazda3 SP25 GT
about 50% of the times i leave the vehicle it does not lock the doors automatically. Dealership states there is no problems and is working OK

Just wondering if anyone as also experienced this problem and what was done to rectify,

This is the 2nd SP25GT since 2015 and I automatically expect car to lock on leaving and therefore often come back to the car and find it unlocked. I have to remember to now check if it locks when leaving but sometimes forget and this is my problem

 

I personally hate that feature; one of my wife's cars has it- - -but I have no explanation why it would be sporadic.

Maybe clean whatever contacts are closing when the door is shut; if the car doesn't know the door is shut it logically wouldn't try to lock the doors.

 

I love the feature working in a bad neighborhood but it would be less than worthless if it was not dependable.

for me, it works 100% of the time at work but 75% otherwise. I think the issue is related to how I leave the vehicle. If a passenger has a door open when I walk away it does not lock. When I open the trunk or a back door before walking away it does not lock. I have developed a habit of listening for the click whenever I walk away.

See if you find a correlation between these or other factors

 

It happens on ALL of their cars. In addition to mine, the 3 loaners ive had also do it. Your body can shield electronic signals to a point. I have mine hanging off a key lock on my belt and even though its not in a pocket, can be blocked at times.

 

I turned this feature off, I found it to be absolutely annoying because while working on it in the garage it became a hassle. If I need the car locked I'll lock it myself.

 

I have a 2016 Mazda3 and it does it once in awhile. I have found opening the door and closing it a bit harder usually sets the auto lock.