What it means
The BMS detects at least one cell with voltage above the safe upper limit. Risk of cell damage from overcharge.
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 tracks cell or cell-group voltage throughout a hybrid or EV battery pack. This code sets when at least one monitored cell exceeds the system's upper voltage limit, prompting protection against overcharging and possible pack damage.
Common causes
Most likely first.
- Cell balancing failed - cell overcharged
- Cell with reduced capacity reaches voltage limit early
- 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 BMS codes, then identify the highest reported cell voltage and whether it occurred during charging, regeneration, or driving.
- Compare the high cell's reading with other cell readings and review its voltage trend using approved scan data.
- Inspect accessible BMS sensing connectors and wiring for damage or poor connections, following the manufacturer's high-voltage safety procedures.
- Check the pack's balancing status and temperature data to see whether balancing failure or a cell reaching its limit early is involved.
- If the high reading persists and wiring is sound, have the affected cell group and pack assessed using the manufacturer's approved battery test.
Common fixes
- Repair a confirmed BMS sensing wire or connector fault causing a false high reading.
- Correct an identified charging or regeneration control fault that is pushing the cell above its limit.
- Service or rebalance the pack if the manufacturer permits it and testing confirms imbalance.
- Replace the affected cell module or pack component if testing confirms reduced capacity or damage.
Can I keep driving?
Stop charging and limit driving if a high-cell warning, charging restriction, or reduced-power message appears; overvoltage can damage the cell and may cause the system to shut down. Arrange prompt battery-system diagnosis.
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.