What it means
The BMS detects that overall cell balancing performance is below expectation. Multi-cell imbalance increases despite balancing efforts.
At a glance
- Usually lights the check-engine light
- The engine or gearbox may go into limp mode
How it works
The battery management system balances cell-group voltages to reduce differences across the high-voltage pack. This code sets when the voltage spread continues to grow or remains greater than expected despite balancing, which can indicate aging balancing circuits, cells with widely different capacity, or a pack nearing its imbalance limit.
Common causes
Most likely first.
- Multiple balancing circuits aged
- Cells severely aged - capacity spread
- Pack cell imbalance approaching service threshold
Symptoms
- EV/hybrid system warning light on
- Reduced power output or limp mode
- Charging may fail or be slowed
- Reduced electric range
How to diagnose it
- Save freeze-frame data and review battery-management records for cell-group voltage spread and balancing activity.
- Compare cell-group voltage differences during charging and operation to determine whether imbalance is persistent or increasing.
- Check charging history and available battery data for groups that repeatedly diverge despite balancing commands.
- Have the balancing circuits and their connections assessed using the manufacturer’s specified battery-pack procedure.
- If the balancing hardware passes, have the pack evaluated for aged or capacity-mismatched cell groups.
Common fixes
- Repair a poor connection affecting the battery balancing system.
- Service or replace failed balancing circuits identified by testing.
- Rebalance the pack if permitted by the manufacturer and appropriate for the measured cell condition.
- Repair or replace battery modules with confirmed capacity mismatch.
Can I keep driving?
Avoid long trips if power is reduced or charging is restricted, because the vehicle may enter limp mode as the imbalance worsens. Electric range and charging performance may decline, so arrange diagnosis soon.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.