What does it mean?
B1664 is a Body (airbags, seat belts, body electronics) fault code. It indicates: Rear Fog Lamp Control Circuit High .
Symptoms
- Rear fog lamp does not light although the indicator in the cluster comes on
- Lamp failure warning displayed after switching on the rear fog lamp
- Function returns temporarily when the bulb is turned in the holder
- Rear fog lamp works only when the vehicle is stationary and fails over bumps, which suggests a broken wire
- Reduced visibility of the vehicle from behind in fog, and a possible inspection failure
Likely causes
- Rear fog lamp bulb burned out or missing from the holder
- Corroded or burnt bulb holder that has lost contact pressure
- Open circuit in the control wire, frequently in the flexing loom between the body and the tailgate
- Poor or missing ground at the rear fog lamp assembly
- Short to battery on the control wire caused by an incorrectly wired trailer socket or accessory
- LED conversion whose current draw is below the detection threshold of the module
- Open output driver inside the lighting control module
How to fix it
- Switch the rear fog lamp on and confirm that it really stays dark
- Remove the bulb and check both the filament and the holder contacts for corrosion or heat damage
- Fit a known good bulb of the correct type and retest
- Measure the voltage at the holder while the lamp is commanded on and carry out a voltage drop test on the ground side
- Unplug the lamp and check the control wire for continuity to the module and for battery voltage that should not be present
- Pay special attention to the flexing wiring between the body and the tailgate, where broken strands hide inside intact insulation
- Repair or renew the holder and harness, and only then consider the lighting control module