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P0303

Cylinder 3 misfire detected

The ECU has detected repeated combustion misfires associated with cylinder 3.

What this code means

The ECU has detected repeated combustion misfires associated with cylinder 3.

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
  • Loss of power

Checks to make

  1. Check related misfire codes
  2. Inspect cylinder 3 ignition components
  3. Compare coil or injector operation with another cylinder where appropriate
  4. Check compression if needed

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.