P0303 Honda Civic
Cylinder 3 Misfire Detected · Powertrain Code · High · Repair: Moderate
What is P0303?
Misfire detected in cylinder 3. Typically caused by a worn spark plug, bad ignition coil, faulty fuel injector, or low compression in that cylinder.
When the Honda Civic triggers code P0303 (cylinder 3 misfire detected), it typically points to an issue in the powertrain system. This is a high severity code, so address it promptly to avoid further damage or safety concerns. Below you'll find the most common causes, symptoms, and repair options specific to the Honda Civic.
This repair is rated moderate, meaning some experience and specialty tools required.
Diagnostic data on this page is compiled from publicly available repair resources and technical service bulletins. Always have a qualified mechanic confirm the diagnosis before authorizing repairs on your Honda Civic.
Common Causes on Honda Civic
- Worn spark plug on cylinder 3 (NGK OE iridium)
- Failed coil-on-plug ignition coil for cylinder 3
- Carbon deposits on cylinder 3 intake valves (DI engines)
- Fuel injector fault on cylinder 3
- Valve adjustment needed (especially on older K-series engines)
Symptoms
- Flashing Check Engine Light during active misfire
- Vibration felt in steering wheel and cabin
- Loss of power
- Rough or uneven idle
- Fuel smell from unburned fuel in exhaust
Notes for Honda Civic
Honda recommends valve adjustment every 60k miles on K-series engines — tight valves are a common misfire cause that is often overlooked.