On Tuesday morning my wife went to the car, unlocked it using the remote and went to open the driver side rear door to put her bag on the floor. Her usual procedure, but the door wouldn’t open. Tried locking and unlocking a few times but no joy. On returning home I tried with the same result!  I was sure I could hear the ‘lock mechanism’ actuating but still the door wouldn’t open using either the outside or inside handles.Tried the obvious activating and deactivating the child lock with no difference. I assumed some sort of rod mechanism had become detached, but I’m not familiar with how the system works, so just a guess.

I’m fairly adept at car maintenance having been in the industry for 40 years but my age and infirmity means struggling to remove the door panel from inside with the door closed is sadly beyond me now! Went my local garage and they were up for the task and booked for Monday. This morning we were off to do some shopping and my wife jokingly said shall I try the door? It opened no problem, and I’ve tried locking and unlocking it many times and it’s fine.

i haven’t cancelled the booking yet, just in case, but does anyone have any idea what’s up?

While your situation with the passenger door lock is quite extreme, I would hazard a guess that your car battery State Of Charge is or was very low.

Normally once the battery SOC falls below 55% then the car will disable the passenger door(s) unlocking to save power. This of course does not usually involve not been able to open the door from the inside, which is not normal and could potentially be dangerous.

Use a multimeter and measure your battery terminal voltage about one hour after you park the car. Check it against the table below.

How old is the car battery ? If 4 years or more then it is probably in need of replacement.

Battery did go through my head, but why only one door, and why did it decide to work today? The car hadn’t been driven since Sunday when it failed to work on Tuesday. I admit I did a few miles on Wednesday but failed to check whether it was okay when I got home. I’ll check the battery as you suggest. I regularly charge it as I know it doesn’t do many miles. Still on the original battery!

2 minutes ago, Mike1947 said:

Still on the original battery!

Well past it's "Best Before" date 🤣

Battery tested as 12.20v. Perhaps get the garage to change it rather than take the door apart and see what happens.