What does it mean?
B1668 is a Body (airbags, seat belts, body electronics) fault code. It indicates: Reverse Lamp Control Circuit High .
Symptoms
- Reverse lamps do not light when reverse gear is engaged
- Very poor visibility behind the vehicle when reversing at night
- Reversing camera picture is dark although the camera itself works
- Lamp failure message in the cluster when reverse is selected
- Reverse lamps work intermittently and cut out as the tailgate is opened and closed
Likely causes
- Reverse lamp bulbs burned out or loose in their holders
- Corroded bulb holder contacts inside the rear lamp cluster, a common result of water ingress
- Open circuit in the reverse lamp control wire, especially in the flexing loom that enters the tailgate or boot lid
- Poor or broken ground at the rear lamp assembly
- Short to battery on the control wire from an incorrectly wired trailer socket or reversing camera installation
- LED reverse lamps whose current draw is below the detection threshold of the module
- Open output driver inside the control module
How to fix it
- Engage reverse with the ignition on and check whether either reverse lamp lights at all
- Remove the bulbs and inspect the filaments, holders and contacts for corrosion or heat damage
- Fit known good bulbs of the correct type and retest, since both bulbs failing together produces this pattern
- Measure the voltage at the holder with reverse selected and do a voltage drop test on the lamp ground
- Disconnect the lamp and check the control wire for continuity to the module and for battery voltage that should not be present
- Inspect the wiring inside the tailgate flex loom, where broken strands hide under intact insulation
- Repair the harness or renew the holder, then verify operation in both rear lamps and clear the code