One problem related to air bag light on has been reported for the 2009 BMW 335. The most recently reported issues are listed below.
When a passenger is belted - with car running/driving - an alarm comes on - basically not recognizing when belted. Also the inactive airbag light is not on. When no passenger, the car used to light up the 'airbag not active' - it no longer shows that (light is always off) whether passenger there or not.