Front Air Bag Sensor Control problems of the 2009 Saturn Aura

The passenger air bag seat sensor does not sense at all times a 130 lb adult is sitting in the seat so it disables the passenger air bag. I paid the gm dealer to have the passenger seat cushion sensor replaced and now the problem has returned. The problem is intermittent and I must look over to see if the sensor detected a passenger before I proceed driving. I talked to the dealer but they do not want to cover the cost of the passenger seat air bag sensor . The last time I had it replaced at the gm dealer it cost me several hundred dollars.