P0307
Moderate severityCylinder 7 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 engine starts shaking or losing power.
What does the P0307 code mean?
The P0307 code means your engine computer has detected that cylinder 7 is misfiring — the fuel in that cylinder isn’t burning properly. The computer notices because the crankshaft slows down very slightly every time cylinder 7 fails to fire.
P0307 only appears on engines with seven or more cylinders, which in practice means V8s and larger — common on trucks, full-size SUVs and performance cars. Because the code names the exact cylinder, you know where to look: the cause is almost always spark (plug or coil), fuel (injector), or compression at cylinder 7. If several cylinders misfire at once, you may also see P0300.
Can you keep driving with a P0307 code?
Yes, for short distances — but don’t put it off. A steady misfire can overheat the catalytic converter, and on a V8 that often means replacing an expensive converter on one side of the exhaust. You may notice a rough idle, shaking at stoplights, or hesitation when towing or climbing hills.
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 P0307 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 7)Check 1st
- Failing ignition coil or coil boot (cylinder 7)Check 2nd
- Clogged or leaking fuel injector (cylinder 7)Check 3rd
- Vacuum leak near cylinder 7 or low compressionCheck last
V8 manufacturers number their cylinders differently. On most GM V8s, the odd cylinders (1, 3, 5, 7) are on the driver’s side; on most Ford V8s, cylinders 5 to 8 are on the driver’s side. In both cases cylinder 7 usually sits at the back of the engine near the firewall, where heat is highest and access is tighter — check a diagram for your exact engine before buying parts.
How to diagnose a P0307 (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; misfires on several cylinders point toward something shared, like fuel pressure.
- Pull and inspect the cylinder 7 spark plug. Look for a worn electrode, oil fouling, cracked porcelain, or wet fuel.
- Swap the cylinder 7 ignition coil with another cylinder on the same bank and clear the code. If the misfire follows the coil, the coil is bad.
- If the misfire stays on cylinder 7 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 worn lifter, burnt valve or head gasket leak.
P0307 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 |
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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P0307 — Frequently asked questions
Is it safe to drive with a P0307 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.
Where is cylinder 7 on my engine?
It depends on the manufacturer. On most GM V8s it is at the back of the driver’s side; on most Ford V8s it is also on the driver’s side, near the back. Always check a diagram for your exact engine.
What’s the difference between P0300 and P0307?
P0300 means a random or multiple-cylinder misfire. P0307 points to one specific cylinder — number 7 — which makes the cause much easier to find.
How much does it cost to fix a P0307?
Often $20 to $150 for a spark plug or $100 to $350 for an ignition coil, depending on your vehicle.
Related codes
General guidance based on the standard SAE definition of the P0307 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.