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ENRUDEPLES

P0304 — Cylinder 4 Misfire Detected

serious

What it means

The engine control module has detected misfire in cylinder 4: the charge in that cylinder is not burning, or burns only partially. Detection is based on crankshaft angular acceleration measured by the crankshaft position sensor over each power stroke. The car shakes at idle, hesitates under load and burns more fuel; a flashing lamp indicates misfire severe enough to overheat the catalytic converter.

Likely causes (most common first)

  1. Worn or fouled spark plug in cylinder 4
  2. Failed ignition coil or cracked high voltage lead on that cylinder
  3. Clogged or leaking fuel injector, dirty injector nozzle
  4. Vacuum leak at the intake gasket, PCV hose or brake booster line
  5. Low compression: burnt or tight valve, worn rings, head gasket leak between cylinders
  6. Wiring damage or an ECM driver fault in the coil or injector circuit

Can you drive with it?

You can reach a workshop at low load, but with a flashing lamp stop: unburned fuel is melting the catalyst.

This is the generic meaning. What about your car?

The same code has different typical culprits on different engines. Tell the AI your make, model and year — it will rank the causes for your exact car and give you a check order.

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