the problem is allmost certainly dirty contacts on the air bag wiring connections. These are found under the front passanger seats. slide the seat forward and you will see the connectors there are two (yellow) the first one is easy to get at just unclip it and clean with wd 40. this will probably cure the fault , if not there is a second connector actually fixed to the underneath of the seat . I had this happen to my modeo and a kind ford machanic showed me ! keeps going off about every 18 months hey ho!
steve210560
September 2009