Cylinder 7 Misfire Detected
P0307 indicates that the engine control module (ECM) has detected a misfire in cylinder 7. A misfire occurs when the air-fuel mixture in the cylinder fails to ignite properly, causing a loss of power, increased emissions, and potential damage to the catalytic converter. Common causes include faulty spark plugs, ignition coils, fuel injectors, or low compression. This code is often accompanied by rough idling, hesitation, and a check engine light.
1. Most Common Causes
- Worn, fouled, or damaged spark plug on cylinder 7
- Faulty ignition coil for cylinder 7 (or corresponding coil unit in COP/DIS systems)
- Clogged, leaking, or electrically defective fuel injector on cylinder 7
- Low compression in cylinder 7 (rings, valves, head gasket)
- Unmetered vacuum leak near the intake port of cylinder 7
- Open or short in the wiring or connector of the coil/injector circuit for cylinder 7
- Faulty PCM (rare)
2. Symptoms You Will Notice
- Check engine light illuminated
- Engine misfire, rough idle, or hesitation during acceleration
- Reduced fuel economy and power
- Engine may shake or vibrate noticeably
3. Step-by-Step Diagnosis
Step 1: Scan the vehicle for codes and note freeze frame data.
Step 2: Inspect spark plug and ignition coil on cylinder 7; swap with another cylinder to see if misfire follows.
Step 3: Check fuel injector on cylinder 7 for proper operation (e.g., using a noid light or swapping injectors).
Step 4: Perform a compression test on cylinder 7 and compare to other cylinders.
Step 5: Inspect for vacuum leaks using a smoke machine or propane enrichment.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive long distances with a misfire, as it can damage the catalytic converter and other engine components. Short trips to a repair shop are acceptable if the misfire is not severe.
How much does it cost to fix?▼
The cost varies depending on the cause. Replacing a spark plug or ignition coil typically costs $50-$150 per part plus labor. Fuel injector replacement can be $150-$400. Compression repairs can be significantly more expensive.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.