If your vehicle is showing passenger airbag off light stays on when an adult is sitting in the seat, here are the most likely causes and the parts you'll need to fix each one.
Aftermarket seat covers pulled too tight can lift the occupant's weight off the sensor. Similarly, objects jammed under the seat can physically interfere with the weight sensor's reading.
The wiring harness connecting the seat weight sensor to the vehicle's computer can get kicked, stretched, or disconnected when the seat is moved back and forth or during interior cleaning.
The weight sensor or fluid bladder inside the seat cushion can fail over time, often due to spilled liquids, heavy localized pressure (like kneeling on the seat), or general wear. It is frequently serviced as part of the lower seat assembly.
The seat weight system can lose its baseline calibration, often after a battery replacement, seat removal, or module update. The system requires a recalibration using a professional diagnostic scan tool.
The computer module responsible for processing the seat sensor data and commanding the airbag system has suffered an internal electronic failure.