What does it mean?
B1634 is a Body (airbags, seat belts, body electronics) fault code. It indicates: Left High Beam Control Circuit High .
Symptoms
- Left high beam does not work while the right one does
- Lamp out warning in the cluster, sometimes only when the high beams are selected
- Uneven and short reach of the main beam at night
- Function returns for a while after the connector is reseated
- Automatic high beam assist, where fitted, stops switching over
Likely causes
- Burned out left high beam bulb, which is the most common single cause
- Loose, corroded or spread terminals in the headlamp connector so the bulb is not properly connected
- Open circuit in the control wire between the module and the left headlamp
- Short to battery on the control wire, often from an incorrectly wired accessory or a repair splice
- LED or discharge conversion that the module cannot recognise as a valid load
- Failed output driver inside the lighting control module
How to fix it
- Switch the high beams on and check the left lamp, then substitute a known good bulb before anything else
- Inspect the connector for pushed back or burnt terminals and check the terminal tension
- Measure the voltage on the control wire at the headlamp with the high beams commanded on and compare it with the right side
- With everything switched off, check the same wire for continuity to the module and for unexpected battery voltage
- Check and clean the headlamp ground, because a poor ground can also make the output read high
- Repair the harness or renew the connector body and terminals, then confirm the code does not return after several on and off cycles
- Replace the control module last, and only if a correct load is connected and the output is still wrong