Sorry, the NHTSA has not posted this TSB document yet.
You can still get the detailed info from Chevrolet for this TSB. Call your local Chevrolet dealer's service department & ask for a copy of TSB# PIC-5157.
CHEVROLET: WHERE AN ILLUMINATED AIR BAG WARNING OR SERVICE AIR BAG MESSAGE ARE NOTED. DTC B0021 MAY BE SET. THE RATE OF THIS OCCURRENCE COULD INCREASE WHEN THE FRONT PASSENGER SEAT HAS BEEN LOWERED. *PE