[eye30]

On my old, now son's, car the rear passenger door lock is not unlocking. 
It happens to be the nearside which is used the most. 

Even when you try to open it manually from the inside the rocker switch moves out to the open position but it does not activate the unlocking gear within the door.

If you pull the rocker switch out and hold your finger on the rocker switch and press the remote - unlock/lock door - you can feel the mechanism move but it just won't open.

A quick look would indicate that the door panel will have to be removed but before this is done anyone had similar?

ps:
Car out of warranty since last September
Child lock deactivated

[Dazzler]

I suspect one of your actuators has died (The electronic solenoid switch that triggers the lock) Hopefully they won't slug your son too much being that it is a common problem with Hyundais. If something has just become detached then obviously it will be a cheaper fix 

[beerman]

I would hit an auto electrician.

Will be cheaper than Hyundai, Shouldn't cost too much remove the door cover and its plug and play from there (A quick google search found the genuine part from a stealer for $120).

Another forum favourite would be to hit the moving parts with some silicon spray just in case it is something sticking. You might get lucky.

[eye30]

Another forum favourite would be to hit the moving parts with some silicon spray

This is the first try as it was working OK so wondering if jamming due to the cold weather we have had..