The lock on one of the doors of my 2014 Panda does not respond to central locking:

• It is permanently in a locked state.

• The locked state can be overridden by using the door handle inside the car, but as soon as the handle has been released it springs back into the locked position.

• The door cannot be opened by the exterior handle.

This is the third time that this has happened:

• On the first occasion, when the car was only a few months old, the back nearside lock failed in this way and was repaired by a Fiat garage.

• On the next occasion, shortly before the warranty expired, the front nearside lock failed in this way and was repaired by a Fiat garage.

• This third occasion is a failure of the replaced mechanism on the front nearside door.

The local Fiat dealer has now closed, and I therefore need to travel quite a distance to get to a Fiat garage, so I'm wondering whether this could be carried out by a non-Fiat garage, or even by me myself.

Can anyone tell me what part is failing, and point me in the direction of instructions for undertaking the job?