OBD-II code guide
P0303 Cylinder 3 Misfire Detected
P0303 indicates a misfire isolated to cylinder 3.
What it means
Cylinder 3 is not burning the air-fuel mixture reliably.
Common symptoms
- Rough running
- Reduced power
- Check engine light
- Shaking under load
- Hard starting in some cases
Likely causes
- Spark plug wear
- Coil failure
- Fuel injector fault
- Vacuum leak
- Mechanical valve or compression problem
First checks
- Record all codes before replacing parts.
- Compare cylinder 3 plug and coil condition.
- Check for coolant or oil contamination on the plug.
- Stop driving if misfire is severe.