Occupant sensors in front seats may stop air bag deployment when a low weight reading indicates a child who could be harmed by the airbag. Some sensors have been fooled due to seat breakdown or composition of materials reacting differently at various temperatures.
Background
Some airbags signaled by seat sensor not to deploy if passenger weight under 105 lbs
Original airbags deployed w/ force powerful enough to kill / injure small adults, children seated in front passenger seat
“Smart” or “advanced” airbags phased in starting MY2004
Installed in all passenger vehicles by MY2007