What does it mean?
B1780 is a Body (airbags, seat belts, body electronics) fault code. It indicates: Occupant Classification Sensor Front LH Circuit Malfunction .
Symptoms
- Airbag warning lamp on and the occupant detection system out of service
- Passenger airbag status indicator stuck on or off regardless of who is sitting there
- The passenger airbag may be disabled even with an adult in the seat
- Weight or occupant status data missing or clearly wrong on the scan tool
- Fault often appears immediately after seat removal, refitting or a deep clean
Likely causes
- Sensor connector under the seat unplugged, half latched or corroded after seat removal or valeting
- Wiring pinched or chafed by the seat rail as the seat is moved
- Water in the carpet reaching the under-seat connector and corroding the terminals
- Load sensor damaged by someone kneeling on the seat, by heavy cargo or by a hard impact on the cushion
- Seat mounting bolts loose or overtightened, changing the preload the sensor sees
- Thick aftermarket seat cover, cushion or object wedged under the seat disturbing the load path
- Occupant classification module fault
How to fix it
- Read the occupant classification codes and view the live sensor values with the seat empty
- Remove seat covers, cushions and anything stored under the seat, then recheck the readings
- Inspect the under-seat connector for corrosion, water marks, backed-out pins and a proper latch
- Move the seat through its full travel while wiggling the loom and watching for signal dropout
- Check the seat mounting bolts are correctly fitted and torqued and that nothing fouls the seat frame
- Carry out the zero or calibration routine the manufacturer specifies for the system; it is required after any seat work
- Replace the sensor or the seat frame sub-assembly as directed, then recalibrate and verify with a known load