What does it mean?
B1644 is a Body (airbags, seat belts, body electronics) fault code. It indicates: Rear Left Turn Lamp Control Circuit High .
Symptoms
- Rear left indicator does not flash while the front one still works
- Indicator flashes much faster than usual and the bulb out message appears
- The lamp works again briefly after the cluster is refitted or the bulb is turned in its holder
- Hazard flashers show the same missing lamp
- Failure at a lighting inspection despite a new bulb being fitted
Likely causes
- Rear left indicator bulb burned out or fitted loosely in its holder
- Corroded bulb holder or a cracked printed circuit board inside the rear lamp cluster
- Broken wire in the rear harness, typically where it flexes into the tailgate, boot lid or quarter panel
- Poor or open ground for the rear left lamp assembly
- Short to battery on the control wire caused by a badly installed trailer socket or accessory
- LED cluster or LED bulb whose current draw is too low for the module to see
- Failed output driver in the lighting control module
How to fix it
- Switch on the indicators and confirm which lamp is dead, then remove the bulb and check the filament and the contact tabs
- Inspect the holder and the cluster circuit board for green corrosion, heat damage or cracked solder joints
- Fit a known good bulb of the specified type and see whether the flash rate returns to normal
- Measure the voltage at the holder while the indicator is on, then do a voltage drop test on the lamp ground
- Disconnect the cluster and test the control wire for continuity to the module and for unwanted battery voltage
- Renew the bulb holder, the cluster or the damaged section of harness as required, and seal any leaks that let water into the lamp
- Replace the control module only after a good bulb and a proven harness still produce the fault