What does it mean?
B1682 is a Body (airbags, seat belts, body electronics) fault code. It indicates: Rear Headlamp Leveling Sensor Circuit Low .
Symptoms
- Headlamps stay in one position, usually aimed low, regardless of load
- Headlamp system warning message displayed at ignition on
- No levelling movement heard from the headlamps when the ignition is switched on
- Poor illumination distance at night because the beams are held down
- Adaptive lighting functions disabled where they are fitted
Likely causes
- Short to ground on the sensor signal wire, often where the loom runs along the rear axle area and is exposed to stones and salt
- Water inside the sensor connector bridging the signal pin to ground
- Open or high resistance reference voltage supply to the sensor, so the signal cannot rise
- Internal short inside the sensor itself after moisture has entered the body
- Harness damaged during suspension, exhaust or towbar work at the rear of the vehicle
- Corroded shared sensor ground point on the underbody
- Failed input circuit in the headlamp levelling module
How to fix it
- Read the sensor voltage on live data; a value stuck at or near zero indicates the signal is being pulled to ground
- Disconnect the sensor and see whether the reported value rises; if it does, the sensor is faulty, if it stays low the wiring is shorted
- Inspect the connector for water, corrosion and green deposits, and dry it before retesting
- With the ignition on, measure the reference voltage and the ground at the sensor connector; a missing reference produces the same symptom
- Measure resistance between the signal wire and ground with the connector disconnected to find a short
- Inspect the harness along the rear axle and around the exhaust for chafing, heat damage and crushing
- Repair the wiring or fit a new sensor as the tests indicate, then carry out the levelling calibration and confirm the beams move with load