Cylinder 12 Contribution/Range Fault
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 |
Code P0300 is a moderate fault. You can generally drive to a workshop, but avoid long trips or high-load driving (motorway, uphill towing) until it is diagnosed. If the code keeps returning after clearing, or if you notice the symptoms listed above worsening, do not delay professional diagnosis. Many moderate codes have multiple possible root causes — a mechanic with live OBD data can identify the exact fault more efficiently than part-by-part trial and error.
Once the fault is repaired, P0300 can be cleared using any OBD-II scanner. Connect the scanner, navigate to "Clear Codes" or "Erase DTCs," and confirm. The check engine light turns off immediately.
The code will return if the root cause was not actually fixed. The ECM re-detects the fault within 1–3 drive cycles and sets the code again.