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Engine misfire

P0304
Cylinder 4 Misfire Detected

One or more cylinders isn't burning its fuel properly. You may feel a shake at idle or a stumble when you accelerate. The misfire is in cylinder 4. Start with that cylinder's spark plug, coil and injector.

Fix it soon

Can I keep driving? For a short while, gently. Have it checked in the next few days, and stop if the car feels, sounds or smells different. Raw fuel from a misfiring cylinder overheats the catalytic converter, which is expensive. A flashing light means that's happening right now.

Common causes

  • Worn spark plugs
  • A failing ignition coil or plug wire
  • A clogged or leaking fuel injector
  • A vacuum leak
  • Low compression from a worn or damaged engine

Listed roughly from most to least likely. The same code can have different causes on different cars.

What to do

  1. If the check engine light is flashing, ease off and stop as soon as it's safe.
  2. Check when the spark plugs were last changed.
  3. On a single-cylinder code, a shop will often swap the coil to another cylinder to see if the misfire follows it.
  4. Have it fixed promptly.

General guidance. Your owner's manual wins. If a red warning light is on or the car drives differently, stop safely and get help.

Related codes

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