What does it mean?
B1789 is a Body (airbags, seat belts, body electronics) fault code. It indicates: Headlamp Leveling Motor Control Circuit High .
Symptoms
- Headlamp aim frozen at one position and unaffected by the level adjuster
- One or both lamps aiming visibly too high, dazzling oncoming drivers
- Lighting warning message on vehicles that monitor the system
- No motor movement or noise during the ignition-on self test
- Automatic levelling does not respond when the vehicle is loaded
Likely causes
- Levelling motor connector unplugged or half latched after headlamp removal or bulb replacement
- Broken conductor in the harness where it flexes between the body and the headlamp
- Corroded terminals in the motor connector after water has entered the headlamp housing
- Internally open winding in the levelling motor so the control unit sees no load
- Control wire shorted to a live feed where it chafes against another circuit
- Blown fuse or open supply to the levelling system
- Lighting control unit output stage failure
How to fix it
- Read the codes and observe both levelling motors during the key-on self test
- Check the fuse and supply feed for the levelling system
- Inspect the motor connector for corrosion, moisture, unlatched housing and backed-out pins
- Measure the resistance of the motor windings at its connector and compare left with right
- Test the control wire from the module to the motor for continuity and for voltage from another circuit
- Flex the harness between body and headlamp while watching the live data for dropouts
- Repair the harness or replace the motor, then reset the system and check the headlamp aim; the control unit is the final suspect