What does it mean?
B1686 is a Body (airbags, seat belts, body electronics) fault code. It indicates: Vehicle Speed Sensor Fault – CAN Signal .
Symptoms
- Speedometer reads zero or jumps around while driving
- Cruise control cannot be engaged and switches itself off
- ABS and stability control warning lamps illuminated along with other systems
- Speed sensitive functions behave incorrectly, such as steering assistance, automatic wipers or speed dependent volume
- Automatic transmission shifts harshly or holds a gear
- Automatic door locking at speed no longer works
Likely causes
- Faulty wheel speed sensor or output speed sensor feeding the module that transmits the speed message
- Damaged sensor wiring near a wheel arch or the gearbox, where heat, water and movement attack the loom
- The transmitting module has its own faults stored and stops sending a usable value
- Corroded connector or a broken wire in the network circuit between the modules
- Poor module ground or low system voltage causing messages to be lost
- Incorrect configuration after a module replacement, or wheel and tyre sizes that do not match the coded values
- Internal failure of the module that generates the speed signal
How to fix it
- Scan every module and record which ones report speed or communication faults, then follow the module with the original fault rather than the one complaining
- Compare the speed values reported by different modules on live data during a road test
- Check the wheel speed sensors and their wiring, paying attention to the flexing sections near the wheel arches
- Inspect the network wiring and connectors for corrosion, damage and any accessory that has been tapped into the bus
- Measure the module supply voltage and carry out voltage drop tests on the module grounds
- Confirm the vehicle configuration matches the fitted wheels, tyres and final drive after any module replacement
- Repair the wiring or replace the proven faulty sensor, then verify that all modules see the same road speed