OBD-II FAULT CODE
P0309
Cylinder 9 Misfire Detected
Meaning, symptoms, likely causes, diagnostic checks and repair guidance for P0309.
- Check Engine light, rough idle, hesitation, flashing MIL if severe
- Worn spark plug
- Faulty ignition coil
- Injector or fuel issue
- Vacuum leak
- Low compression
- Scan all modules and record freeze-frame data before clearing codes
- Check battery voltage and related fuses
- Identify affected cylinder(s), inspect plugs/coils, check fuel trims and compression if needed
- Swap-test coil/injector where practical, replace worn ignition parts, repair vacuum/fuel/compression cause
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Disclaimer: Information is provided for general guidance only and may not apply to all vehicles. Always consult a qualified technician.