What does it mean?
B1516 is a Body (airbags, seat belts, body electronics) fault code. It indicates: Battery Current Sensor Performance .
Symptoms
- Charging voltage swinging up and down instead of holding steady
- Stop-start function disabled or working only occasionally
- Battery or charging system message in the driver display
- Accessories shutting down soon after the engine is switched off
- Complaints of a flat battery after the car stands for a day or two
Likely causes
- Sensor nut on the negative battery post loose, dirty or corroded, giving a poor connection
- Extra ground leads or accessory earths bolted directly to the battery post, bypassing the sensor so it never measures that current
- Broken or chafed sensor pigtail, or a connector full of corrosion
- Battery replaced without being registered or reset, so the charging strategy no longer matches the sensor data
- Aged or weak battery giving readings that fail the plausibility test
- Internal drift or failure of the current sensor itself
- Fault on the serial line between the sensor and the module that reads it
How to fix it
- Inspect the sensor where it clamps to the negative battery cable and clean the post and clamp faces properly
- Confirm that every ground and accessory lead lands on the correct side of the sensor, not directly on the post
- Retighten the sensor and terminal hardware to specification, avoiding over-tightening the plastic body
- Check the sensor pigtail and connector for breaks, corrosion and moisture, and repair as needed
- Compare the current value in scan data against a clamp meter reading with a known load switched on
- Test the battery and, if it has been replaced, register or reset it as the vehicle requires
- Replace the sensor with its cable assembly if it still reads incorrectly, then clear the code and recheck