Cylinder 2 Misfire Detected
Cylinder 2 isn't firing properly, like one spark plug in a four-cylinder engine refusing to ignite the fuel-air mixture. The engine computer detected this misfiring and turned on the check engine light to alert you.
The ECU monitors crankshaft speed variation between each cylinder firing using the crankshaft position sensor. When cylinder 2 fails to combust properly, it creates an abnormal dip in RPM that the computer detects. If misfire counts exceed the threshold within a specific drive cycle, the fault is logged.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Crankshaft acceleration | Consistent RPM variation within 2-3% | Deviation >5% on cylinder 2 over 1000 revolutions |
| Misfire count per 1000 cycles | <1 misfire | >5-10 misfires detected |
Code P0303 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, P0303 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.