BYD BY012: BYD BYD Battery Management System Error Code B...

Symptoms

The battery pack temperature has exceeded 60C (140F). The BMS disconnects the battery and the thermal management system activates maximum cooling.

Cooling system failure: fan, pump, or thermal management module not operating
Excessive charge or discharge current generating heat faster than the system can dissipate
Ambient temperature exceeding the rated 45C maximum
Internal cell short circuit causing thermal runaway in one or more cells

Step 1: Check the thermal management system: fans, pumps, and coolant flow
Repair or replace failed cooling components immediately
Step 2: Allow the battery to cool to below 40C before attempting any operation
Monitor the temperature trend; if it continues rising, the pack may be in thermal runaway
Step 3: If temperature rises without load, isolate the pack and evacuate the area
Thermal runaway in lithium batteries can cause fire and toxic gas emission
Step 4: After cooling, perform a cell-by-cell voltage and impedance test
Replace any cell with abnormal voltage or impedance

Reset: The BMS reconnects the battery once the temperature drops below 45C and all cell voltages are verified normal.

Q: What is thermal runaway?
An uncontrolled exothermic reaction in a lithium cell where rising temperature accelerates the reaction. Once started, it cannot be stopped and may spread to adjacent cells.
Q: What is the maximum battery temperature?
Most lithium batteries: 60C alarm, 65C shutdown. Storage: -20C to 45C. Charging: 0-45C. Discharging: -20C to 60C.
Q: How do I prevent thermal events?
Maintain the cooling system, respect charge/discharge current limits, avoid high ambient temperatures, and use a properly configured BMS.