I have done some searching but mostly get results for the lock cylinder failure that's common, so I decided to ask!

Its a 2003 Civic LX coupe. We got the car used at 36000 miles. It has power locks, but no module for the use of a remote. We found very quick that using the key in the locks was not going to work for long. The key would barely work in either door. Upon searching we found the lock cylinders wear horribly and were the likely issue. Rather then have to replace both and the ignition, to have the same key, we looked into a factory remote and learned it was not optioned on our car. With the factory add on prices, we opted for an alarm instead. Crisis averted.

Fast forward almost 100,000 miles... well we noticed by accident that the drivers door was now not locking with the alarm. Wtf... I check & passenger side works... I try the power switch. Passenger works but nada on the driver. Lock actuator. I decide well for now I will use the key again on it. Well I could not budge the key in the lock. Neither lock or unlock. So i pushed the interior manual door lock. Well it was no longer a light push like before. You have to ram it down. If you then use the switch or deactivate the alarm, still a no go on the drivers door. Passenger glides easy and works flawlessly...

I have had switches in other cars fail or actuators fail... but neither ever led to making the manual locking becoming stiffer to the point of this. I have heard Honda's use air pressure to flip the lock is that true?

So what do you think? Car has not been slim jimmed that I know of. No one broke in. Switch, actuator, lock cylinder, something wonky with the rods?

Doing this on my phone so please forgive any typos I might have missed

 

The wires between the door and the frame of the car tend to break from repeated flexing from opening the door. Clearly you're going to have to take the door apart to see what's going on. This sort of stuff is often caused by someone trying to break in.

It's electric, there is no air system involved.