OBD-II trouble code
P0306: Cylinder 6 Misfire Detected
The engine computer detected a misfire specifically in cylinder 6. This code only applies to engines with six or more cylinders. Diagnosis is more targeted than P0300 — the bad part is on or feeding cylinder 6.
Quick facts
- System
- Powertrain
- Category
- Ignition and Misfire
- Severity
- High severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $50 – $1,500
- DIY difficulty
- Intermediate DIY
What does P0306 mean?
A misfire is a cylinder that fails to combust properly. The engine control module (ECM) detects misfires by monitoring crankshaft speed — a healthy combustion event accelerates the crankshaft slightly, and the ECM watches for the missing acceleration that signals a failed combustion event. When the ECM isolates the misfire to a single cylinder, it sets a cylinder-specific code instead of the generic P0300.
P0306 means the misfire is in cylinder 6. This code only applies to engines with six or more cylinders — inline-6, V6, V8, V10, and V12 configurations. On an inline-6, cylinder 6 is the last cylinder, at the rear of the engine near the firewall. On a V6, cylinder 6 is commonly the last cylinder on Bank 2 in many configurations. On a V8, the position depends on the manufacturer — Ford and GM use different cylinder numbering schemes. Check your engine's service information for the exact location.
A flashing check engine light during P0306 indicates the misfire is active. Unburned fuel reaches the catalytic converter and can damage it quickly. Pull over safely if the light is flashing. If the light is steady, drive directly to a shop and avoid hard acceleration.
Common causes
- Worn or fouled spark plug in cylinder 6
- Failing ignition coil for cylinder 6 (most common on coil-on-plug engines)
- Faulty fuel injector for cylinder 6 (stuck, clogged, or leaking)
- Low compression in cylinder 6 from a burned valve, worn rings, or head gasket leak
- Cracked or damaged spark plug wire feeding cylinder 6 (older engines)
- Carbon buildup on the intake valve for cylinder 6
- Vacuum leak isolated to the cylinder 6 intake runner
- Improperly installed or wrong-gap spark plug
Symptoms
- Check engine light on or flashing
- Rough idle and engine shaking
- Loss of power on acceleration
- Hesitation or stumble
- Poor fuel economy
- Smell of unburned fuel from the exhaust
- Engine running on one fewer cylinder than designed
Diagnostic steps
- 1.Confirm the code is P0306 alone — companion misfire codes on the same bank may indicate a shared cause like fuel pressure or a vacuum leak.
- 2.Inspect the spark plug in cylinder 6. Compare its condition to the other plugs.
- 3.Swap the ignition coil from cylinder 6 with a known-good coil. Clear the code and drive. If the misfire follows the swapped coil, that coil is bad.
- 4.Repeat with the spark plug.
- 5.Test the cylinder 6 fuel injector resistance and confirm pulsing.
- 6.If ignition and fuel test fine, perform a compression test on cylinder 6.
Repair cost
$50 – $1,500
Single spark plug $10 to $30 plus 15 to 30 minutes of labor. Ignition coil $40 to $200 plus brief labor. Fuel injector $100 to $400 plus 1 to 3 hours. Cylinder 6 is often at the rear of the engine and may be difficult to access — on transverse V6 layouts the rear cylinders sit against the firewall, requiring extra labor for plug, coil, or injector work. Compression-related repairs $1,000 and up.
Estimate your repair
Run the numbers for your vehicle
Open the Repair Cost Estimator with spark plug replacement preselected. Adjust labor rate and vehicle category to fit your situation.
DIY vs shop
This is an intermediate DIY job. It usually involves diagnostic steps, specialty parts, and some careful work in tight spaces. If you have the tools and a service manual or trustworthy video for your specific vehicle, it is achievable in a weekend. Otherwise, a competent independent shop will be faster.