What does it mean?
B1678 is a Body (airbags, seat belts, body electronics) fault code. It indicates: Passenger Courtesy Lamp Control Circuit High .
Symptoms
- Passenger side courtesy lamp stays dark while the other interior lamps work
- No footwell illumination on that side when the door is opened at night
- The lamp comes on briefly when the door is at a certain angle, which points to a broken wire
- Illuminated entry does not work on the passenger side
- The fault started right after interior trim or audio system work
Likely causes
- Bulb burned out or the courtesy lamp assembly removed and not refitted
- Broken wire in the passenger door harness, usually inside the flexing boot at the hinge
- Connector unplugged or a terminal pushed back after glove box, trim or audio work
- Corroded holder contacts that no longer touch the bulb base
- LED interior bulb whose current draw is below what the module can detect
- Short to battery on the control wire from an incorrectly connected accessory
- Open output driver in the body control module
How to fix it
- Open the passenger door and confirm the lamp is dead, then fit a known good bulb or lamp unit
- Inspect the holder contacts for corrosion and weak spring pressure
- Make sure the connector is fully latched and no terminal has been pushed out of the housing
- Measure the voltage at the lamp connector while the module commands the lamp on with the door open
- Check continuity through the door hinge boot while flexing the loom, since broken strands hide inside undamaged insulation
- Refit an original type bulb if an LED conversion has been installed
- Repair the broken conductor, then cycle the door several times and clear the code to confirm the repair