Trouble codes › P0303

P0303 Cylinder 3 Misfire Detected

Ignition and misfire

P0303 means cylinder 3 is misfiring, usually from a bad spark plug, ignition coil or fuel injector on that cylinder.

The engine computer has seen cylinder 3 fail to fire often enough to set a code. The cylinder numbering depends on the engine; check your service information for the layout.

Can I keep driving? Not if you can avoid it.

If the check-engine light is flashing, stop driving as soon as you safely can to protect the catalytic converter. With a steady light and a mild miss, drive gently and get it fixed soon.

Common causes

  1. A worn or fouled spark plug in cylinder 3
  2. A failing ignition coil or plug wire on cylinder 3
  3. A clogged or leaking fuel injector on cylinder 3
  4. A vacuum leak near cylinder 3
  5. Low compression in cylinder 3 (less common)

Symptoms

  • Rough idle or shaking
  • Loss of power
  • Flashing or steady check-engine light

Known problems: GM V8 AFM/DFM lifter failure · 5.7L Hemi lifter and camshaft wear ("Hemi tick") · Honda 3.5L V6 VCM misfires and fouled spark plugs

What to check first

  1. Swap the cylinder 3 coil with another cylinder and see whether the misfire moves.
  2. Inspect the spark plug.
  3. Check the injector and look for vacuum leaks near that cylinder.
  4. Do a compression test if the coil, plug and injector check out.

What does P0303 mean on your vehicle?

The likely cause depends on your engine. iRepair researches your exact year, make, model and engine (service bulletins, recalls and owner reports) and tells you what to check first. Your first 3 questions are free.

Ask iRepair about P0303

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Related codes

General guidance for P0303 on most vehicles. Some makers use the same code a little differently; confirm in the service information for your vehicle, put safety first, and see a professional when in doubt.