P0306
Moderate severityCylinder 6 Misfire Detected
You can drive short distances, but fix it soon — a persistent misfire dumps unburned fuel into the exhaust and can damage your catalytic converter. If your check engine light is flashing, the misfire is active and severe: stop driving.
Stop driving if: the check engine light is flashing, or the car starts shaking or running noticeably worse.
What does the P0306 code mean?
The P0306 code means your engine computer has detected that cylinder 6 is misfiring — the fuel in that cylinder isn’t burning the way it should. The computer spots this by watching the crankshaft: every time cylinder 6 fails to fire, the crankshaft slows down for a split second.
You’ll only see P0306 on engines with at least six cylinders (V6, inline-six, V8 and up). Because the code names the exact cylinder, diagnosis is easier than with a random misfire: you know precisely where to look. A single-cylinder misfire almost always comes down to one of three things at that cylinder — spark (plug or coil), fuel (injector), or compression. If several cylinders misfire at once, you may also see P0300.
Can you keep driving with a P0306 code?
Yes, for short distances — but don’t ignore it. A steady misfire can overheat and ruin the catalytic converter, which turns a cheap spark plug job into a repair costing well over $1,000. The car may also idle rough, hesitate, or lose power, especially going uphill or under load.
A flashing check engine light is always different. It means the misfire is bad enough to damage the converter right now. Pull over safely and stop driving.
What causes a P0306 code?
Listed in the order most shops would check them — cheapest and most likely first, not as statistical odds. The real cause varies by year, make, model and engine.
- Worn or fouled spark plug (cylinder 6)Check 1st
- Failing ignition coil or coil boot (cylinder 6)Check 2nd
- Clogged or leaking fuel injector (cylinder 6)Check 3rd
- Vacuum leak near cylinder 6 or low compressionCheck last
Cylinder numbering differs between manufacturers, so check a diagram for your exact engine before buying parts. On many front-wheel-drive V6 engines, one bank of cylinders sits against the firewall under the intake manifold — if cylinder 6 is on that rear bank, replacing its plug or coil takes far more labor, which is why quotes can vary so much.
How to diagnose a P0306 (check these first)
Work from the cheapest, most likely cause to the most expensive:
- Scan for other codes. Lean codes (P0171, P0174) point toward a vacuum leak; other misfire codes point toward something shared, like fuel pressure.
- Pull and inspect the cylinder 6 spark plug. Look for a worn electrode, oil fouling, cracks in the porcelain, or wet fuel.
- Swap the cylinder 6 ignition coil with a neighbouring cylinder and clear the code. If the misfire moves to the other cylinder (for example P0304), the coil is bad.
- If the misfire stays on cylinder 6 after swapping the coil and plug, check the fuel injector — listen for its click with a mechanic’s stethoscope or have a shop test it.
- Still misfiring? A compression or leak-down test rules out a mechanical problem such as a burnt valve or head gasket leak.
P0306 repair cost
Costs vary a lot by vehicle and region. These are typical US ranges including parts and labor — treat them as a ballpark for the conversation with your shop, not a quote.
| Spark plug replacement | $20 – $150 |
| Ignition coil replacement | $100 – $350 |
| Fuel injector replacement | $200 – $600 |
| Vacuum leak repair | $100 – $400 |
| Rear-bank plug or coil (intake removal) | $250 – $600 |
Tools & parts that help
An OBD-II scanner with live data confirms which cylinder is misfiring and lets you watch the misfire counter after you swap a coil — so you know the fix worked before you buy anything else. A coil and plug for one cylinder are usually inexpensive.
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P0306 — Frequently asked questions
Is it safe to drive with a P0306 code?
For short distances, yes, but fix it soon. If the check engine light is flashing, stop driving — an active misfire can destroy the catalytic converter.
How do I know if it’s the coil or the spark plug?
Swap the cylinder 6 ignition coil with another cylinder and clear the code. If the misfire code follows the coil to the new cylinder, the coil is bad. If it stays on cylinder 6, suspect the spark plug or injector.
What’s the difference between P0300 and P0306?
P0300 means a random or multiple-cylinder misfire. P0306 points to one specific cylinder — number 6 — which makes the cause much easier to find.
How much does it cost to fix a P0306?
Often $20 to $150 for a spark plug or $100 to $350 for an ignition coil. It costs more if cylinder 6 sits under the intake manifold on your engine.
Related codes
General guidance based on the standard SAE definition of the P0306 code. A real diagnosis depends on your make, model, year, engine and other symptoms. This is not a substitute for a professional inspection — when in doubt, have a technician confirm the cause before replacing expensive parts.