Why has the tailgate on my Hyundai Is35 stopped locking when I lock the car with a smart key?

Locking/Unlocking the doors from the outside
This is done using the RENAULT Card; see the "RENAULT Card" information in Section 1.
In certain cases, the RENAULT card may not work:
- if the RENAULT card battery is weak, flat, etc.
- if equipment operating on the same frequency as the card (mobile phones, etc.) is used;
- vehicle located in a high electromagnetic radiation zone.
It is then possible:
- to use the key integrated into the card to unlock the front left-hand door;
- to lock each of the doors manually;
- to use the interior door locking/unlocking control (refer to the following pages).
Using the key integrated in the RENAULT card
Insert key 1 into the lock in the driver's door and lock or unlock. Locking the doors manually
Turn screw 2 with the door open (using the end of the key) and close the door.
This means that the doors are then locked from the outside.
The doors may then only be opened from the inside or by using the key in the front left-hand door. Interior locking/unlocking door control
Switch 3 controls the doors, boot and, depending on the vehicle, the fuel filler flap simultaneously.
If a door or the tailgate is open or not closed properly, the doors and tailgate lock/unlock quickly.
If you need to transport objects with the boot open, the other opening elements can still be locked: with the engine stopped, press switch 3 for more than five seconds to lock the other opening elements.
Locking the doors without the RENAULT card
For example, in the event of a discharged battery or the RENAULT card temporarily not working, etc.
With the engine switched off and an opening element (door or boot) open, press and hold switch 3 for more than five seconds.
When the door is closed, all the doors and the tailgate will be locked.
Unlocking the vehicle from the outside is only possible with the RENAULT card in the vehicle's access zone or using the key integrated in the RENAULT card.
Door and tailgate status indicator
With the ignition on, the warning light integrated in switch 3 informs you of the locking status of the opening elements:
- indicator light on, the doors and tailgate are locked,
- indicator light off, the doors and tailgate are unlocked.
When you lock the doors, the indicator light remains lit and then goes out.

I do not think your daughter pressing the lock has caused the problem but you never know ? try unlocking it with the key if it hass a external lock ,it it hasnt then you will need to clamber in the back and unbolt the body hasp if this is possible if not you will have to remove the rear panel on the tailgate and open it that way ,its possible that the cables in the rubber shroud have broke at this instance as the tailgate was closed .Difficult to say without a good look and a play so if you cannot get it to open with the key then consult a local mechanic to have a look for you .

Have you tried using the key at the tail gate, ,open with the key then move then push the locking mechanism open with a screwdriver the latch close while the door/gate was open, push it back open use some force. Hope this help if is a mechanical issue and not electrical it doesn't matter .

I would have used the lock mechanism from old tailgate. has it been deadlocked?

The lock actuator motor is most likely sticking due to corrosion, open up the tailgate and replace the electric power lock actuator motor. If you need instructions on how to access the inside parts you can get them here for small subscription fee.

If this is an original equipment replacement part should work just like its predeceser before the accident. Just check that everything is wel connected and in place by removing the panels and take a look inside.

Try a graphite lock lubricant. It works better than wd40

Had a similar problem, found the tailgate was not closed all the way. Close the tailgate real hard and then lock with the key fob.

the barrel is faulty and needs replaced

sounds like the tumbler is bad, try to replace it yourself , if you have an electronic chip in your key you have to go to dealer to get it installed. cheapest way to fix this is order a new locking tailgate handle from jc whitney or somewere and replace the whole thing.