P0303: Cylinder 3 Misfire Detected
Do not keep driving
A flashing light calls for stopping as soon as it is safe. With a steady light, drive gently and get the cylinder diagnosed before the catalytic converter takes the damage.
What this code means
Combustion is failing in cylinder 3. On V-configuration engines it is worth noting which bank cylinder 3 sits on before ordering parts, since numbering differs between manufacturers and the cylinder nearest the front of the car is not reliably cylinder 1. Confirm the physical location against the engine's own firing order rather than assuming.
Likely causes
Start here
- Faulty ignition coil · easy
- Worn or fouled spark plugs · easy
- Clogged fuel injectors · moderate
Less common
- Damaged spark plug wire or boot · easy
- Vacuum leak in intake manifold or hoses · moderate
Rare
- Low engine compression · specialist
- Burnt or leaking valve · specialist
Symptoms
Components involved
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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What makes one worth reading:
- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
- What actually fixed it — or that nothing did, which is worth knowing too.
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