What does it mean?
B1399 is a Body (airbags, seat belts, body electronics) fault code. It indicates: STPS (Seat Track Position Sensor) - Passenger Short or Short to Battery .
Symptoms
- SRS lamp on with a passenger seat position circuit fault
- Scan tool value pegged high and unaffected by seat movement
- The fault may only be present while the passenger seat heater or seat motor is in use
- Passenger airbag deployment force falls back to its default setting
- No effect on engine performance
Likely causes
- Signal wire chafed onto a powered passenger seat circuit such as the seat heater feed
- Aftermarket under-seat wiring installed alongside the restraint and sensor circuits
- Signal and supply wires shorted together where the under-seat loom is crushed on the rail
- Water in the seat connector bridging the signal pin to a live pin
- Terminal pushed back in a multi-way plug and contacting a powered pin
- Sensor internally shorted to its own supply
- Airbag control module input fault
How to fix it
- Determine whether the fault tracks the use of a particular seat function, which identifies the source of the voltage
- Power the restraint system down safely and wait the discharge time before disconnecting
- Remove any aftermarket wiring run under the passenger seat next to the sensor circuit
- With the sensor unplugged and the ignition on, check the signal wire for battery voltage while cycling the seat functions
- Inspect the loom along the rail for flattened sections where two circuits could touch
- Repair the damaged loom and reroute it clear of powered seat wiring
- Replace the sensor only after the harness is proven clean, then confirm the reading follows seat position