What does it mean?
B1643 is a Body (airbags, seat belts, body electronics) fault code. It indicates: Rear Left Turn Lamp Control Circuit Low .
Symptoms
- Rear left indicator does not flash, or stays permanently lit
- Fuse for the rear lighting blows repeatedly
- Indicator flash rate changes and the bulb out warning appears
- Other lamps in the same cluster behave oddly because of corrosion in a shared holder
- Faults come and go over bumps or after rain
Likely causes
- Short to ground in the rear left lamp control wire, often where the loom passes through the quarter panel or a body grommet
- Water sitting in the rear left lamp cluster, corroding the bulb holders and the printed circuit board
- Trailer wiring spliced into the rear lamp circuit, adding load the module cannot support
- Wrong bulb fitted, or a bulb base making contact with the housing
- Crushed harness in the luggage compartment, for example under a spare wheel or a load floor
- Internal short in the rear turn lamp driver of the lighting control module
How to fix it
- Remove the rear left lamp cluster and inspect it for water, corrosion, and burnt or melted bulb holders
- Unplug the cluster and check whether the code still returns, which separates the lamp from the harness
- With the connector disconnected, measure the resistance between the control wire and ground; a low value proves a short to ground
- Follow the loom through the body grommet into the quarter panel and look for chafing or crushed insulation
- Disconnect any trailer or towing wiring temporarily to rule it out
- Repair the harness with sealed joints and refit the correct bulb, then dry and reseal the lamp housing
- Replace the lighting control module only if the output is still low with the harness disconnected