2007 X3 missing back seatbelt

Seat base is not bolted.Grab under front of base with both hands near the ends and just snatch up quickly.Pull the seat base out from the car and the bolts for seat belts are visable.

In the future please be more specific about what you drive. So now I'm going to have to guess what you drive.

OK, 2001 Jetta, three-wire airbag plugs, two wire seatbelt plug (passenger side), four wire seatbelt plug (driver's side). Put in different seats. This is to eliminate the airbag light and restore the order: 1. Connect only positives on airbag plugs with a 4.7Ohm, 1/2 watt, 5% tolerance resistors; 2. Passenger side seatbelt plug: connect with a 2.2K Ohm, 1/2 watt, 5% tolerance resistor; 3. Driver's side seatbelt plug: bundle two positives together (in my case, red and yellow), two negatives together (two browns). Then connect with a 470 Ohm, 1/2 watt, 5% tolerance resistor. 4. Use Vag-Com to clear codes.

The new 2013 Bentley Mulsanne Mulliner has the same thing.I know on the Bat Mobile it means the ejector seat is not fully charged.

The only generic answer I can conclude with information you provide is ;

1) The passenger seat of a newer general motors car

2) The seatbelt light does not light up when the seat is not occupied

3) The passenger side Airbag (SRS) has been turned OFF

4) While occupied , the seatbelt light on the insrument cluster lights steady

5) when the seatbelt is active (buckled with a passenger) the light flashes.

6) anybody?

if the passenger is a skinny little thing they might be triggering the ocupent sensor

How to install a seatbelt in a 2007 GMC envoy in the passenger side

yes if you visit the scrapyard ,easy job to renew ,look under the back seat in case the middle belt is under the seat

These 3 codes have to do with restraint system.
B2292 Seatbelt pretensioner fault.
B2293 Passenger front airbag fault.
B2691 Seatbelt buckle switch circuit fault Ft.driver side.

clean seat belt with suitable cleaner. most of the time it doesnt slide through top piviot due to dirt build up

You can normally unplug the sensor that is on the floor under the seat, either attached or close to seatbelt.