Who diagnosed a u/s airbag? I wouldn't lose heart just yet. Most of the time, airbag warning lights are down to flaky connections. If your car h afteras seat side airbags (check for a little 'airbag' tag sewn into the side bolster of the backrest), look for a small orange connector on the floor immediately next to the front/LHS of the left-most front passenger seat. Disconnect the car battery, leave for about 20 minutes, then pull connector apart & give it a squirt of WD40. Plug/unplug the connector a good few times after that to clean up the contact surfaces.
There's a similar connector(but yellow this time) for the passenger side dash airbag, under the panel with 'airbag' sewn into it.
Both of these are covered by old forum threads, with photos and instructions. Do a search restricted to the Multipla section and you'll soon find them. I would post links but it's a PITA on a phone.....
Good luck!