Prius (Gen 3) :: Airbag Only Works 50% Of The Time With Passenger In Front Seat

The passenger airbag light only works 50% of the time there is a passenger in front seat. I've moved the seat forward and backward .. But ultimately the passenger must unbuckle, step out if the car , and sit back down in order for it to work. I took it to the dealer with its silver warranty package and the dealer can't find a code so won't fix it. "If it keeps doing it, come back." I'm not going to drive 20 miles out of the way, on one if the 50% chance days that it doesn't work.