What does it mean?
B1685 is a Body (airbags, seat belts, body electronics) fault code. It indicates: Left Headlamp Leveling Motor Control Circuit Performance .
Symptoms
- Left headlamp beam is stuck high or low while the right side adjusts normally
- Buzzing, clicking or grinding noise from the left headlamp when the ignition is switched on
- No self test sweep of the left beam at ignition on
- Headlamp system warning message in the cluster
- Uneven beam pattern that dazzles oncoming traffic on one side only
Likely causes
- Seized or stripped levelling actuator inside the left headlamp, where the plastic gears wear out
- Broken ball joint between the actuator shaft and the reflector, so the motor turns but the reflector does not move
- Moisture inside the left headlamp housing corroding the actuator and its connector
- High resistance in the actuator supply or ground wiring, so the motor moves too slowly to satisfy the module
- Reflector mechanism jammed after a headlamp repair, an impact or the fitting of an incorrect bulb assembly
- Levelling system not calibrated after a headlamp or module replacement
- Failed motor driver stage inside the levelling control module
How to fix it
- Switch the ignition on and observe both headlamps during the self test; note whether the left beam moves at all
- Command the actuator with a scan tool if the function is available and watch the reflector
- Remove the actuator or its cover and check whether the shaft turns while the reflector stays still, which indicates a broken ball joint or stripped gears
- Inspect the headlamp housing for condensation and water, and check the actuator connector for corrosion
- Measure the supply and ground at the actuator during a commanded movement, and do a voltage drop test if the motor is slow
- Compare the left and right actuator behaviour, since the good side is the best reference
- Replace the actuator or the affected mechanism, then run the levelling calibration and confirm both beams move together