What does it mean?
B1809 is a Body (airbags, seat belts, body electronics) fault code. It indicates: Passenger Door Lock/Unlock Switch Circuit Stuck Unlock .
Symptoms
- Vehicle does not stay locked and unlocks on its own
- Alarm cannot be armed or disarms by itself shortly after locking
- Actuator noise from the passenger door while the car is parked
- Auto-lock while driving no longer works
- Battery drain caused by continuous actuator commands
Likely causes
- Unlock contact stuck closed or contaminated inside the passenger switch pack
- Moisture bridging the unlock contact after a torn vapour barrier or blocked drains
- Unlock signal wire shorted to ground
- Chafed harness in the passenger door hinge boot
- Aftermarket central locking wiring holding the unlock line active
- Passenger door module input stuck in the active state
How to fix it
- Watch the unlock status in live data with nobody touching the switch
- Unplug the passenger switch pack and check whether the status goes inactive
- Measure the unlock contact resistance at rest
- Inspect the door for water and repair the vapour barrier if it is torn
- Ohm the unlock wire to ground with the module disconnected
- Disconnect any aftermarket alarm or locking module and repeat the test
- Replace the switch pack or repair the harness, then confirm the vehicle stays locked