Airbag light passenger stays on

[BodeTA]

I have an  avensis 2010. The airbag light stays on. I have checked the connections under seats. I have been able to narrow the issue. When there is nothing on the passenger seat everything is fine. The moment the passenger seat is occupied (also a 2kg bag) few seconds later the light comes on. I tried further while driving I hit the seat with my hand and the light came up again. I did the same again while parked, same result. Any idea what could be faulty and if an easy/non-expensive fix? 

[Devon Aygo]

Which light is coming one?

The red SRS warning light on the instrument cluster in front of the driver ( there is a fault )

The orange Passenger airbag mode light in the centre console ( normal it indicates if the passenger airbag is on or off when the seat is occupied )

[BodeTA]

3 minutes ago, Devon Aygo said:

Which light is coming one?

The red SRS warning light on the instrument cluster in front of the driver ( there is a fault )

Yes, it is the red SRS warning light. And this is when the passenger seat is "occupied". What part could be fault at the seat?

[Devon Aygo]

Just a thought, do as you have been and add weight to the seat to bring the light on then plug the passengers seat belt in, does the light go out?

[BodeTA]

This was simulated on Sunday when I picked someone up without switching off the engine. The person wore the seat belt but the light remained on

[Devon Aygo]

OK then the car needs plugging in to a diagnostic computer to see what fault code is being set with the warning light.