What does it mean?
B1633 is a Body (airbags, seat belts, body electronics) fault code. It indicates: Left High Beam Control Circuit Low .
Symptoms
- Left high beam stays dark when the main beams are switched on
- Blue high beam indicator in the cluster lights up although only one lamp works
- Lighting fuse blows repeatedly, or the module cuts the output after a few seconds
- In some short circuit patterns the left high beam stays on permanently
- Very poor illumination when flashing the lamps to overtake
Likely causes
- Short to ground on the left high beam control wire, typically where the harness rubs against a bracket or the radiator support
- Water and salt inside the left headlamp connector creating a leakage path
- Bulb of the wrong rating or an aftermarket lamp drawing more current than the driver allows
- Damaged bulb socket with the terminals touching the reflector or the housing
- Pinched wiring after front end repair or bumper removal
- Internal short in the high beam driver of the lighting control module
How to fix it
- Check whether the code returns with the left headlamp connector unplugged, which separates the lamp from the wiring
- Inspect the connector and socket for burnt terminals, moisture and corrosion
- With the connector unplugged and the circuit switched off, measure the resistance between the control wire and ground; a low reading proves a short to ground
- Move the harness along its route while watching the meter to find a chafed spot, paying attention to the area behind the headlamp and along the front panel
- Verify that the fitted bulb matches the specification and remove any aftermarket lighting spliced into the circuit
- Repair the damaged wiring with sealed joints, then clear the code and test the high beams several times
- Replace the lighting control module only if the output is still low with the harness disconnected