One cylinder isn't contributing power equally to the others, like one piston in an engine doing less work than its neighbors. The ECU detected this imbalance by monitoring combustion variations across cylinders.
The ECU uses crankshaft speed variations between cylinder firings to calculate each cylinder's power output. When one cylinder misfires or burns fuel poorly, it creates a distinctive dip in engine speed that the ECM detects. If cylinder 12's contribution falls outside the expected range compared to other cylinders, the fault sets.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Cylinder Power Balance | ±5-10% variation between cylinders | >15% deviation from average cylinder contribution |
| Crankshaft Speed Variance | Smooth acceleration between teeth | Abnormal dips during cylinder 12 firing event |