What does it mean?
B1663 is a Body (airbags, seat belts, body electronics) fault code. It indicates: Rear Fog Lamp Control Circuit Low .
Symptoms
- Rear fog lamp does not light when it is selected
- Rear fog lamp stays on permanently, even with the lights switched off
- Rear lighting fuse blows repeatedly
- Rear fog indicator in the cluster does not match what the lamp is actually doing
- Other lamps in the same cluster misbehave because of shared corrosion or a shared ground
Likely causes
- Short to ground in the rear fog lamp control wire, often in the loom that runs into the tailgate or along the rear valance
- Water inside the rear lamp cluster or the separate rear fog lamp housing
- Corroded bulb holder allowing the contact to touch the reflector or the body
- Non standard bulb or added lighting connected to the rear fog circuit
- Crushed wiring in the luggage compartment or under the rear trim
- Damaged wiring at a trailer socket where the rear fog output is used
- Internal short in the rear fog output driver of the lighting module
How to fix it
- Select the rear fog lamp and check with live data whether the module is commanding the output
- Remove the rear fog lamp holder and inspect it for water, corrosion and burnt contacts
- Disconnect the lamp and see whether the code returns, which separates the lamp from the harness
- With the lamp unplugged, measure the resistance from the control wire to ground; a low reading confirms a short
- Trace the wiring through the rear body grommet and inside the tailgate, checking for chafed insulation
- Disconnect any trailer socket wiring temporarily to eliminate it as a source
- Repair the harness, dry and reseal the lamp housing, then verify normal operation and clear the code