What does it mean?
B1638 is a Body (airbags, seat belts, body electronics) fault code. It indicates: Right High Beam Control Circuit High .
Symptoms
- Right high beam stays dark while the left one lights normally
- Bulb out message that appears only when the main beams are selected
- Main beam pattern clearly biased to one side of the road
- Intermittent operation that changes when the headlamp connector is moved
- Automatic high beam function disabled where the vehicle is equipped with it
Likely causes
- Right high beam bulb burned out or missing
- Poor contact in the headlamp connector caused by corroded, spread or heat damaged terminals
- Open circuit in the control wire between the lighting module and the right headlamp
- Broken ground for the right headlamp assembly
- Short to battery on the control circuit from a badly wired accessory or a previous repair
- LED retrofit that draws too little current for the module to detect a valid lamp
- Faulty lamp driver in the body control module or smart junction box
How to fix it
- Test with a known good bulb of the correct type, since a burned filament is the most frequent cause
- Inspect the socket and connector for corrosion, discoloured terminals and a loose fit
- Command the high beams on and measure the voltage at the bulb terminals, comparing the values with the left headlamp
- With the connector disconnected, test the control wire for continuity to the module and for unwanted battery voltage
- Do a voltage drop test on the headlamp ground and clean the ground stud if needed
- Remove any LED conversion and refit an original type bulb, then see whether the code clears
- Repair the open or the short in the harness, and consider the control module only after the circuit is confirmed good