I consulted a Citroen techie about my airbag light staying on and he told me 90% of these are due to the connectors under the seat. He suggested cleaning and reseating them (batt disconnected and left for 10+ mins first!) several times if necessary but this only fixed my fault for a few hours. His next suggestion - they fix them by cutting out the connector altogether & join the wires using pre-soldered bullet sleeves with heat-shrink tubing on top. I just soldered them and spun some insulating tape around each soldered joint and the light always goes out now
If anyone has this fault but can't solder, I'd be happy to do it for them if you're in my area.