What does it mean?
B1771 is a Body (airbags, seat belts, body electronics) fault code. It indicates: Passenger Side Buckle Switch Circuit Malfunction .
Symptoms
- Belt reminder chime and lamp stay on with the belt fastened, or never come on at all
- Passenger belt shown as unbuckled on the display while it is clearly latched
- Airbag warning lamp may also light because the restraint strategy depends on this input
- Occupant detection behaves oddly, for example the passenger airbag status indicator switching at the wrong time
- Fault appears or disappears as the passenger seat is slid forward and back
Likely causes
- Coins, crumbs or other debris pushed into the buckle mouth holding the switch in one state
- Drink spilled into the buckle, corroding or sticking the internal contacts
- Worn internal switch after years of use, giving an unstable resistance
- Buckle harness pinched or chafed where it passes the seat rail as the seat moves
- Corroded under-seat connector after water ingress or carpet cleaning
- Buckle from a different specification fitted during a seat swap, so the resistance no longer matches
- Restraint or body module input stage failure
How to fix it
- Read the codes and watch the buckle status live while latching and releasing the belt several times
- Shine a light into the buckle mouth and remove any coins, wrappers or debris
- If a pretensioner is built into the buckle, disarm the restraint system before unplugging anything
- Measure the resistance or continuity of the buckle switch in both latched and released states and compare with specification
- Wiggle the buckle harness through the full seat travel while watching the live value for dropouts
- Inspect and clean the under-seat connector, repairing corroded terminals
- Replace the buckle assembly if it tests out of specification; change the module only after the circuit is proven