1.4 Polo SE 2006 4 door. weird central locking problems

[TLS145]

I recently bought this car second hand, and at first everything worked fine. But today I noticed the central locking being really unreliable. All 4 doors make a noise like they're locking/unlocking when I hit the button, but they only sometimes actually change between being locked/unlocked. Putting the key in the door only unlocks the drivers door, so that's the only one I can reliably lock or unlock. Is there anything I can easily do myself to troubleshoot or fix this, or am I just going to have to take it to a repair shop?

[Crasher]

It is possible the car has aftermarket central locking as you do not mention a remote control, if you private message me your registration number I will check the build spec. If it is factory central locking, you should start with a fault code read of the central convenience system as this will accurately tell you what is wrong. Mrs Crasher’s Polo 9N is the same age and her passengers door was acting up, the only solution was a new lock unit which is not an easy job and the part was £183.22. It only opening the drivers door could be a coding feature to prevent someone jumping in the passengers door and this can be turned off but if this is the case, two operations of the drivers door lock will unlock the other doors.

[TLS145]

I'm pretty sure it's a factory system, I just forgot to mention the remote. How would I find that fault code?

I don't think it's that feature where only the driver's door opens on the first click, at least when locking it remotely, since all of the doors lock/unlock at random when I hit the button on the key and it doesn't seem to matter how many times I hit the button. But if I put the key in the door and turn it twice, all of the doors lock/unlock except for the rear driver side door, which just stays locked. So at least I know I'm able to reliably lock the doors now, which was my biggest concern.

[Crasher]

Code read time.