What it means
The cell balancing circuit M reports a stuck on 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 controls the equalization path for the battery cell group assigned to channel M. The battery management system checks whether that path turns off when M is no longer commanded on. This code sets when the M path appears to stay active, potentially pulling that group away from the voltage of the others.
Common causes
Most likely first.
- Balancing switch or driver stuck on
- Shorted 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
- Review freeze-frame data and live M-channel command and cell-group voltage to confirm whether the path was reported active when M should have been off.
- Compare the M group’s voltage trend with neighbouring groups and check whether it changes as the M command changes.
- With the high-voltage system made safe using the vehicle’s service procedure, inspect M-channel wiring and connectors for shorts, chafing, or damaged pins.
- Test the M balancing switch and circuit for a conducting path when commanded off, following the manufacturer's procedure and specification.
- If the M switch and wiring pass, have the battery management system driver output for channel M tested for a stuck-on condition.
Common fixes
- Repair shorted or chafed wiring or connector damage in the M balancing circuit.
- Replace the M balancing switch or component if it remains on when commanded off.
- Repair or replace the battery management system driver if its M output is stuck on.
Can I keep driving?
Arrange prompt service because a balancing path that remains on can disturb the M cell group and trigger power or charging limits. Avoid long trips, and if power is restricted or limp mode begins, stop safely and have the hybrid or EV system checked.
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.