Possible, sure, but I don't believe any car has that as an oem option you can simply select. Meaning you'd have to physically do the mod yourself. Not sure why you'd want it but you must have a reason. Too lazy to use the remote? Or maybe the lights flashing when you use the remote are too annoying, which is a gripe of mine. My car has the dealie where you simply touch the door handle and it'll lock, which is close to what you want. Since you're already right there it isn't much extra effort to touch it.
Or maybe your car is older with no remote? If so then I'd imagine you can just push the lock down before you close the door?
On all the cars I've tinkered with there is a link rod between the handle inside and the actual lock on the door, so you pull the handle and it unlocks the door but it won't relock. If locked and the link were not there you can't get out... Ask me how I know Point being you have to unlock it to get out, so you need it re-lock automatically.
I would take advantage of the oem lock solenoid and tie it to the door switch so when you open the door it locks it. You just need to tie it in with a timer so it doesn't burn up the solenoid or drain the batt if you leave the door open. Like when you push the lock button it give power for a second and stops. Long enough to be certain it locks, but no longer. I kinda recall the same deal if you hold the lock button down? If so it means you could tie the door open switch to the lock push button and it should work.
I'm sure there's a way to do it via software, but that's a needle in a haystack imo. I wouldn't even know where to start but you might search the net because people have discovered various tweaks and shared them. I've seen some on youtube too, but yours in an odd request so I'd wager no?
So give us more detail, like why not use the remote, why do you want this feature and do you want it on all the time?
The only scenario I'd want if for is extra hot days in the summer where it's so hot that I want to leave the AC on while I shop. The last thing I want after a walk on >150F asphalt in >100F ambient temp is to get into a >150F car. With my older Benz it was easy, but all my newer ones are designed to prevent locking yourself out when it's running. I assume it's because for every person that wants that feature, thousands of others will lock themselves out of their car. Plus safety. "Safety first"... I HATE that saying. So I'd image there would be a lawsuit for every idiot who did that with a baby in the car, which would somehow be the car mfg's fault. Like if I cut myself with a knife it's clearly the knife mfg's fault. This is why my beautiful all back interior has a big bight yellow warning the visor about airbags.
Ok, done ranting, but know that I could on and on
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