Cylinder 6 Misfire Detected
Diagnostic trouble code P0306 indicates that the powertrain control module (PCM) has detected a misfire in cylinder number 6. The PCM monitors the crankshaft position sensor to measure the rotational speed of the crankshaft, and a variation in speed during the power stroke of cylinder 6 triggers this code.
A misfire can cause significant drivability issues and potentially damage the catalytic converter if unburned fuel enters the exhaust. It should be diagnosed and repaired as soon as possible, especially if the check engine light is flashing.
Common symptoms
- Check engine light illuminated or flashing
- Rough idle or engine hesitation
- Lack of engine power during acceleration
- Noticeable engine vibration or shaking
- Decreased fuel economy
Likely causes
- Faulty or worn spark plug in cylinder 6
- Defective ignition coil or spark plug wire for cylinder 6
- Clogged or failing fuel injector on cylinder 6
- Vacuum leak near cylinder 6 intake runner
- Low engine compression in cylinder 6 due to internal wear or valve issues
- Faulty powertrain control module (PCM) or wiring issues (rare)
What to check before replacing parts
Scan for other codes and check freeze frame data
Look for: Note if the misfire occurs at idle, under load, or at specific RPMs, and check if there are lean/rich codes or multiple cylinder misfire codes that might indicate a broader issue.
Inspect the spark plug and ignition coil for cylinder 6
Look for: Remove the spark plug and check for excessive wear, carbon fouling, or a cracked insulator. Inspect the coil boot for carbon tracking or oil contamination.
Swap the ignition coil from cylinder 6 to another cylinder
Look for: Clear the codes and test drive. If the misfire code moves to the new cylinder (e.g., P0305 if moved to cylinder 5), the ignition coil is faulty.
Test the fuel injector operation for cylinder 6
Look for: Listen for a clicking sound using a stethoscope, or use a noid light to verify the injector is receiving the pulse signal from the PCM. Check injector resistance with a multimeter.
Perform a compression test and cylinder leak-down test on cylinder 6
Look for: Compare the compression reading of cylinder 6 to the other cylinders. A significantly lower reading indicates a mechanical issue such as a burnt valve, blown head gasket, or worn piston rings.
This page explains the generic P0306 definition and is general reference information, not a diagnosis for your specific vehicle. Actual causes, severity, and repairs vary by make, model, engine, and mileage — always confirm with a scan tool and a qualified technician before replacing parts.
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