What does it mean?
B1801 is a Body (airbags, seat belts, body electronics) fault code. It indicates: Driver (Left) Door Lock/Unlock Switch Circuit Low .
Symptoms
- Driver door lock switch does nothing, or doors lock and unlock on their own
- Other switches in the same pack may work while the lock rocker is dead
- Locking only possible with the remote or the key blade
- No actuator click when the lock switch is pressed
- Fault reappears every time the door is opened and closed
Likely causes
- Signal wire from the driver switch pack shorted to ground
- Switch contacts internally shorted or stuck closed by wear
- Water intrusion into the driver door switch pack after a failed vapour barrier or blocked drains
- Harness chafed inside the rubber boot between the door and the A-pillar
- Corroded or green-stained terminals at the door module connector
- Aftermarket alarm or central locking wiring spliced into the switch circuit
- Door module input stage pulling the line low internally
How to fix it
- Inspect the switch pack and door interior for water, corrosion and blocked drain holes
- Unplug the switch pack and measure the signal voltage at the module pin
- If the voltage rises to normal with the switch unplugged, replace the switch pack
- If it stays low, ohm the signal wire to ground with both ends disconnected
- Open the door hinge boot and inspect for broken or chafed conductors
- Clean and tighten the module connector and check the module ground
- Replace the door module only after the short has been proven repaired