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P0301

Cylinder 1 misfire detected

The ECU has detected a combustion misfire associated with cylinder 1.

What this code means

The ECU has detected a combustion misfire associated with cylinder 1.

Possible causes

  • Faulty spark plug or ignition coil
  • Fuel injector problem
  • Low fuel pressure
  • Vacuum leak
  • Low compression or mechanical engine fault

Common symptoms

  • Check engine light
  • Rough idle
  • Poor acceleration
  • Engine vibration
  • Possible flashing engine warning light during an active severe misfire

Checks to make

  1. Check for related misfire codes
  2. Inspect cylinder 1 ignition components
  3. Compare ignition or injector components with another cylinder where appropriate
  4. Check fuel delivery and compression if the fault remains

Safety

  • A flashing engine warning light can indicate a catalyst-damaging misfire. Avoid continued hard driving until the cause is diagnosed.

Model notes

Cylinder numbering differs by engine manufacturer; confirm which physical cylinder is cylinder 1 for the vehicle.