Cylinder 7 Misfire Detected
The P0307 code indicates that the Powertrain Control Module (PCM) has detected a misfire specifically in cylinder number 7. The computer monitors the crankshaft position sensor to measure rotational speed, and sets this code when it detects a lack of acceleration from cylinder 7's power stroke.
A misfire can allow unburned fuel to enter the exhaust, potentially overheating and destroying the catalytic converter. It should be diagnosed and repaired immediately, especially if the check engine light is flashing.
Common symptoms
- Flashing or illuminated Check Engine Light
- Rough idle or engine shaking
- Noticeable lack of engine power or hesitation during acceleration
- Poor fuel economy
- Smell of unburned fuel from the exhaust
Likely causes
- Faulty or worn spark plug in cylinder 7
- Defective ignition coil or spark plug wire for cylinder 7
- Clogged or failing fuel injector on cylinder 7
- Vacuum leak affecting the intake runner for cylinder 7
- Low engine compression in cylinder 7 due to internal mechanical issues
What to check before replacing parts
Read all OBD-II codes and review freeze frame data.
Look for: Note if the misfire occurs under specific conditions (e.g., cold start, high RPM) and check for other codes like lean/rich conditions that might point to a broader issue.
Inspect the cylinder 7 spark plug and ignition coil or wire.
Look for: Look for worn electrodes, carbon tracking, cracked porcelain, or oil/coolant contamination in the spark plug well.
Swap the cylinder 7 ignition coil with a known good coil from another cylinder.
Look for: Clear the codes and test drive; if the misfire code moves to the new cylinder, the ignition coil is confirmed faulty.
Test the cylinder 7 fuel injector operation using a noid light or by swapping it with another cylinder.
Look for: A flashing noid light confirms the PCM is sending the signal; if the misfire moves when the injector is swapped, the injector is clogged or dead.
Perform a compression test and cylinder leak-down test on cylinder 7.
Look for: Compression readings significantly lower than other cylinders indicate internal mechanical damage, such as a burnt valve, blown head gasket, or worn piston rings.
This page explains the generic P0307 definition and is general reference information, not a diagnosis for your specific vehicle. Actual causes, severity, and repairs vary by make, model, engine, and mileage — always confirm with a scan tool and a qualified technician before replacing parts.
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