What does it mean?
B1521 is a Body (airbags, seat belts, body electronics) fault code. It indicates: Buckle Switch Driver Short or Short to Battery .
Symptoms
- Airbag warning lamp on
- Belt reminder lamp and chime stuck in one state, usually as if the belt were always latched
- Belt status in scan data does not change when the buckle is latched or released
- Occasionally a seat circuit fuse blows or a powered seat function stops working
- Code returns straight away after clearing
Likely causes
- Buckle wiring chafed against a powered lead in the seat loom, typically a seat motor, seat heater or memory feed
- Aftermarket seat heater or accessory tapped into the seat harness and shorting into the buckle line
- Terminal backed out of the under-seat connector and touching a live pin beside it
- Water and corrosion inside the seat connector bridging a supply pin to the switch line
- Insulation damaged where the harness passes the seat frame or the rail bolt
- Internal short inside the driver buckle assembly after liquid ingress
How to fix it
- Latch and release the belt while watching buckle status in live data to confirm the signal never moves
- Disconnect the buckle and check the harness side for battery voltage with the key on
- Ask about and inspect any aftermarket seat heater or accessory wiring, and disconnect it for a retest
- Inspect the under-seat connector for corrosion and for terminals touching adjacent live pins
- Follow the seat harness looking for melted or chafed insulation against powered leads
- Repair or replace the damaged harness section with proper terminals and reroute it clear of power feeds
- Replace the driver buckle assembly if the short is proven internal, then clear the code and retest