What does it mean?
B1806 is a Body (airbags, seat belts, body electronics) fault code. It indicates: Passenger Door Lock/Unlock Switch Circuit Stuck Low .
Symptoms
- Passenger door lock switch is dead while the driver switch still works
- Doors lock or unlock without any input
- No actuator movement from the passenger side switch
- Fault sets again as soon as the passenger door is used
- Central locking behaves inconsistently between doors
Likely causes
- Signal wire from the passenger switch shorted to ground
- Switch contacts worn or welded closed inside the passenger switch pack
- Water running down inside the passenger door and reaching the switch or connector
- Harness chafed in the passenger door hinge boot
- Corroded terminals at the passenger door module or at the body-side connector
- Aftermarket wiring tapped into the passenger lock circuit
- Passenger door module input failure holding the line down
How to fix it
- Read the passenger switch state in live data with the switch untouched
- Unplug the passenger switch pack and check whether the input voltage recovers
- Inspect the door interior for water, a torn vapour barrier and blocked drains
- Measure the switch contact resistance in the rest position
- Ohm the signal wire to ground with the module and switch both unplugged
- Open the hinge boot and inspect the conductors while flexing the loom
- Replace the switch pack or repair the harness, module replacement last