What does it mean?
B1781 is a Body (airbags, seat belts, body electronics) fault code. It indicates: Occupant Classification Sensor Front RH Circuit Malfunction .
Symptoms
- Airbag warning lamp lit and the occupant classification system inactive
- Passenger airbag on or off indicator not matching who is actually seated
- Passenger airbag may stay switched off with an adult in the seat
- Live data shows one corner reading zero, negative or far out of step with the others
- Fault typically appears straight after seat removal, refitting or interior cleaning
Likely causes
- Under-seat connector for the sensor loose, corroded or not relatched after work on the seat
- Sensor lead chafed or crushed by the seat rail during normal adjustment
- Moisture from a wet carpet, spilled drink or leaking door seal in the connector
- Load cell damaged by heavy loading, kneeling on the cushion or transport damage
- Seat frame distorted or mounting bolts incorrectly torqued, so the sensor is preloaded
- Seat cover, booster cushion or item jammed between seat and console altering the load path
- Occupant classification module fault
How to fix it
- Read the codes and look at all four corner values with the seat empty; compare them with each other
- Remove aftermarket covers, extra cushions and anything stored under or beside the seat
- Inspect the sensor connector for corrosion, moisture and backed-out terminals, and confirm the lock is engaged
- Wiggle-test the sensor lead through the full seat travel while watching the live value
- Check that the seat frame is not fouling the console or a floor bracket and that the bolts are correctly torqued
- Run the manufacturer's zero or calibration procedure, which is mandatory after any seat disturbance
- Replace the sensor or seat frame assembly as specified, then recalibrate and verify with a known weight