had similar airbag light problem with my facelift 156 JTDm, tried to reset with fancy snap on box of tricks but would not... reading said "passenger curtain airbag squib...value too high"
searched in boot as you guys suggested... and found two connectors one orange and one yellow both attached to yellow cables on offside of boot behind carpet.
disconnected battery and left the car for 30mins,pulled connectors apart and cleaned,then cable tied together with small cable ties.
re-connected battery, restarted car....Bingo
what would i do without AO???