P0307: Cylinder 7 Misfire Detected
Updated November 12, 2026
The engine computer watches crankshaft speed and noticed that cylinder 7 isn't firing properly. Each misfire means that cylinder didn't burn its fuel, so the engine loses power and unburned fuel goes into the exhaust. This code only appears on engines with seven or more cylinders, which in practice means V8s and larger.
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🔧 Want to check this yourself? An OBD2 scanner reads the code; models with live data also show the sensor readings used in the checks below. See code readers and scanners from $24.99 ↓ · Which scanner do I need?
Common causes
- A worn or fouled spark plug in cylinder 7
- A failing ignition coil or plug wire for that cylinder
- A clogged or failing fuel injector, or a loose injector connector
- A vacuum leak near that cylinder, such as a leaking intake manifold gasket
- Low compression from a valve, ring or head gasket problem (less common)
Code meanings can vary slightly by manufacturer. Use these as a starting point and confirm with your vehicle's service information or a mechanic before replacing parts.
Symptoms
- Rough idle or shaking
- Loss of power or hesitation
- A flashing check engine light during heavy misfiring
- Worse fuel economy
Is it safe to drive?
A flashing check engine light means a severe misfire: stop driving as soon as it's safe and have the car towed, because unburned fuel can overheat and ruin the catalytic converter. With a steady light and a mild misfire, drive gently and get it fixed soon.
How to check it with a scanner
- Plug an OBD2 scanner into the port under the dashboard and read all stored codes and the freeze-frame data (the conditions when the code set).
- Find which cylinder is number 7 on your engine; V8 cylinder numbering differs between makers, so check a repair manual or service site.
- With the engine off, swap the cylinder 7 coil (or plug wire) with a neighboring cylinder, clear the code and drive. If the misfire moves to the other cylinder, the coil or wire is the problem.
- Pull and inspect the cylinder 7 spark plug for wear, oil or carbon.
- If spark checks out, inspect the injector connector and have the injector tested and a compression test done on that cylinder.
- After a repair, clear the code and drive normally for a few days to confirm it doesn't come back.
A basic code reader shows the code; scanners with live data let you watch sensor readings, which is what you need for most of the checks above. See OBD2 scanners under $100.
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Questions
What does P0307 mean?
P0307 is the generic OBD2 code for "Cylinder 7 Misfire Detected." The engine computer watches crankshaft speed and noticed that cylinder 7 isn't firing properly. Each misfire means that cylinder didn't burn its fuel, so the engine loses power and unburned fuel goes into the exhaust. This code only appears on engines with seven or more cylinders, which in practice means V8s and larger.
Is it safe to drive with P0307?
A flashing check engine light means a severe misfire: stop driving as soon as it's safe and have the car towed, because unburned fuel can overheat and ruin the catalytic converter. With a steady light and a mild misfire, drive gently and get it fixed soon.
How do I check P0307 myself?
Read the code and freeze-frame data with an OBD2 scanner, then: Find which cylinder is number 7 on your engine; V8 cylinder numbering differs between makers, so check a repair manual or service site. With the engine off, swap the cylinder 7 coil (or plug wire) with a neighboring cylinder, clear the code and drive. If the misfire moves to the other cylinder, the coil or wire is the problem. Pull and inspect the cylinder 7 spark plug for wear, oil or carbon. If spark checks out, inspect the injector connector and have the injector tested and a compression test done on that cylinder.
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