2004 Citroen Xsara Picasso "air bag fault" showing on dashboard

It may only be a bad connection, but it`s best not to mess with these things unless you no what your doing
Try to find a good independant garage, as a main dealer is likely to charge the earth.

If the car has had a shunt before you got it and the airbag system was replaced but the computer not reset, it will display the history of the system every time you run the engine even if the bag and sensor were both replaced with brand new ones the reset is not automatic in which case a main dealer will charge about £50 for the five minutes it takes with a laptop, adaptor box and patch lead. 20mm of black insulation tape over the lamp is a much cheaper fix and if this is the case then the airbag will very likely be fine. many small garages will have the widget and program to do this much cheaper as airbag systems are common to many different cars. They should also be able to run a diagnostic whilst they are at it.

if an airbag or seat belt has deployed you normally require a new ecu. "black tape" is no good as airbag light on is now part of the mot test! get a read done to determine fault because you wouldnt want system to be inoperative in the event of an accident!

most common fault on your car is the seat squib , its the wirng loom underneath the seat after constant moving the seat back and forth it has a bad connection remove battery and wait at least 15 mins before touching wirnig lool (very important )disconnect wiring and replug failing that cut ends of wires and resolder together its akward but is the most common fault