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P0304

Cylinder 4 misfire detected

The ECU has detected repeated combustion misfires associated with cylinder 4.

What this code means

The ECU has detected repeated combustion misfires associated with cylinder 4.

Possible causes

  • Spark plug or ignition coil fault
  • Fuel injector problem
  • Vacuum or intake leak
  • Low compression
  • Fuel-pressure issue

Common symptoms

  • Check engine light
  • Rough running
  • Engine vibration
  • Poor acceleration

Checks to make

  1. Check related codes
  2. Inspect cylinder 4 ignition components
  3. Compare coil/injector behaviour where appropriate
  4. Check compression if the fault remains

Safety

  • Do not replace parts from the code alone. Confirm the fault with live data, wiring checks and manufacturer procedures. Keep clear of hot or moving engine components.

Model notes

The code definition is generic; exact diagnostic thresholds, component locations and repair procedures vary by vehicle.