Re: airbag weight sensor
"ok so i take what dealership is calling the weight sensor is actually oc sensor".
Yes it's grandly titled the Occupant Classification Sensor as it goes beyond just the weight and works out your size, where on the seat you're sitting, forward or back, colour of socks, last underwear change etc
"i dont know what the original fault was so wondering now if this is the same thing or not"
You can have both faults ongoing at the same time but waggling the wiring to the under seat orange connectors tends to make the very common underseat dodgy wiring airbag warning go out
"basically there has been no passengers for over a week and i was out for a drive at the weekend and the light just apperead and now comes on within say a minute of starting and stays on constant"
The OCS sensor, when it's going wrong, tends to go bad real quick until it happens every time you turn on the engine, (often accompanied by mad flashing of the amber pass seat sensing warning) and no waggling of under seat wires will cure it. If your guys have access to examiner then it will show up on there for sure
So looking at OC Sensor replacement £100 plus 30mins to fit