OBD codes / P0309
P0309
SeriousCylinder 9 Misfire Detected
Address promptly — can worsen or affect drivability.
Likely causes
- worn spark plug or ignition coil
- clogged or leaking fuel injector
- low compression on that cylinder
Common fixes
- replace the cylinder 9 spark plug and coil
- test the injector; compression test if it persists
Seeing P0309 on your car? Get a diagnosis specific to your exact year, make and model.
Diagnose P0309 for my vehicleGeneric OBD-II reference. Manufacturer-specific behavior varies — confirm with a scan tool and, for safety-related codes, a professional inspection.