What it means
The cell balancing circuit M reports a stuck off condition. Cell-group voltage equalization may be impaired on this channel.
At a glance
- Usually lights the check-engine light
- The engine or gearbox may go into limp mode
How it works
Balancing circuit M serves the battery cell group assigned to channel M and allows the battery management system to reduce small voltage differences. The module monitors whether the M circuit responds when balancing is requested. This code sets when the M path remains inactive despite that request, so the assigned group may not equalize.
Common causes
Most likely first.
- Open balancing switch or circuit
- Open or damaged balancing-circuit wiring
- BMS driver fault
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
- Check freeze-frame data and live M-channel command and cell-group voltage to establish whether balancing was requested when the fault set.
- Compare the M group’s voltage with neighbouring groups while the M path is commanded on to see whether equalization is absent.
- With the high-voltage system made safe according to the vehicle’s service procedure, inspect the M connector and harness for an open, loose, corroded, or damaged connection.
- Test the M balancing switch and wiring for continuity and poor connections using the manufacturer's procedure and specification.
- If wiring and switch checks pass, test the battery management system driver and its M-channel output.
Common fixes
- Repair an open or damaged M-channel wire or connector.
- Replace a failed M balancing switch or circuit component.
- Repair or replace the battery management system driver if it fails to activate M.
Can I keep driving?
The vehicle may limit power or charging, so avoid long trips and be prepared for reduced electric range. If the vehicle enters limp mode or will not charge, stop safely and arrange prompt service; continued use can increase imbalance in the M cell group.
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.