Check the wiring and plugs under the seat. They are vulnerable to repeated seat travel and vacuum poking. The car could be losing sight of the seat and buckle switches?

 

What's vacuum poking Brendan? I think that is still illegal in Portugal.

 

Good morning
I have an issue on my 2014 mk3 renault scenic passenger seat or seat belt

I don’t plug the seat belt buckle in and sit on the seat and when driving the seatbelt warning light and noise indicate which is correct telling me someone is in the seat without a seatbelt on.

I plug the seatbelt in and sit on the seat and drive off and the same thing happens.
Any suggestions

Could it be another seat with a load on?

 

No all other seats are free

 

Go over all your seats and buckles.
My Qashqai occasionally throws a seat belt warning for no obvious reason, moving the centre buckle on the rear seats seems to cure it

 

It’s the front passenger seat not the rear

 

Good morning
I have an issue on my 2014 mk3 renault scenic passenger seat or seat belt

I don’t plug the seat belt buckle in and sit on the seat and when driving the seatbelt warning light and noise indicate which is correct telling me someone is in the seat without a seatbelt on.

I plug the seatbelt in and sit on the seat and drive off and the same thing happens.
Any suggestions

We could assume that the seat switch is working but the buckle switch is not.
The buckle can get a lot of dirt in which could affect it's operation. That would be the first thing to try.
After that the switch might be broken. It's generally a normally open and the buckle closes it ( some are proximity Hall effect so there is no mechanical bits to push)