What does it mean?
Cylinder balance control, sometimes called smooth running control, compares the crankshaft acceleration produced by each cylinder and trims the injected quantity per cylinder so that every one contributes equally. The module enables that loop only once the engine is warm and stable and the crankshaft signal is clean enough to resolve the contribution of each firing event. This code is stored when the strategy takes longer than the calibrated time after start up to become active. It normally means the crankshaft signal quality is poor, the engine is mechanically or hydraulically uneven, or warm up conditions are never reached.
Symptoms
- Rough idle, worst in the first minutes after a cold start
- Vibration through the body and pedals at low engine speeds
- Diesel knock or a harsher combustion sound than usual
- Visible smoke while the engine is cold
- MIL on, sometimes with injector or misfire codes stored alongside
- Slow warm up and higher fuel consumption on short journeys
Likely causes
- Crankshaft position sensor signal weak, noisy or affected by a damaged reluctor ring
- Genuine mechanical unevenness between cylinders, such as differing compression or a leaking valve
- One or more injectors delivering an incorrect quantity so the balance never settles
- Unstable rail or fuel pressure just after start up
- Thermostat stuck open or a coolant temperature sensor reading low, so the enabling conditions are never met
- A misfire present at start up that prevents the strategy from being enabled
- High resistance or interference in the crankshaft sensor wiring and shielding
How to fix it
- Read every stored code first, since misfire, injector or crankshaft sensor codes usually identify the real problem
- Watch the per cylinder correction or contribution values on a scan tool from a cold start and note which cylinder stands out
- Scope the crankshaft position sensor signal and inspect the reluctor ring for damage or debris
- Perform a relative compression or a cylinder contribution test to separate a mechanical fault from a fuelling one
- Check rail pressure stability during and after start and carry out an injector return flow test where applicable
- Confirm the thermostat closes and the engine reaches normal operating temperature
- Repair the cylinder that is out of balance, then confirm on a fresh cold start that the control loop is enabled within the expected time