P0306: Cylinder 6 Misfire Detected

P0306 means the ECU has detected repeated misfires on cylinder 6. Because cylinder 6 only exists on engines with six or more cylinders, this code is found exclusively on inline-6, V6, V8, and larger configurations. Common culprits are an ignition coil or spark plug specific to cylinder 6, a clogged injector, or in rarer cases compression loss in that cylinder.

P0306 is a misfire-related diagnostic trouble code classified as high severity. When your vehicle's ECU detects this condition, it stores P0306 and illuminates the check engine light.

If your vehicle has triggered P0306, you may notice one or more of these symptoms:

• Check engine light on or flashing
• Noticeable rough idle and vibration through the seats
• Loss of power, especially under load
• Increased fuel consumption
• Possible fuel smell from the exhaust

Here are the most common causes of P0306, ranked by how likely they are to be the culprit:

No - address this immediately. A persistent single-cylinder misfire dumps unburned fuel into the catalytic converter, which can overheat and fail. If the check engine light is flashing, stop driving and have the vehicle recovered to a workshop.

Follow these steps to pinpoint the root cause of P0306:

1. Read freeze-frame data and look at RPM, load, and coolant temperature when the misfire was logged. Cold-only misfires often point to fuel; hot-only misfires often point to ignition coils heat-soaking
2. Swap the ignition coil from cylinder 6 with a coil from a healthy cylinder. Clear codes and drive. If the misfire follows the coil, replace it
3. Remove the cylinder 6 spark plug and inspect for wear, fuel fouling, oil deposits, or a cracked porcelain. Replace any plug that looks suspect
4. Listen to the cylinder 6 injector with a stethoscope. A weak or absent click points to electrical or mechanical injector failure
5. Perform a compression test on cylinder 6 and compare to the others. A difference of more than 10% indicates an internal engine issue requiring deeper inspection

Repair costs for P0306 vary depending on the root cause and your vehicle. Here are typical estimates:

P0306 behaves differently depending on your vehicle. Select your car below for model-specific causes, known issues, and adjusted cost estimates:

These codes are often seen alongside P0306 or indicate related issues: