Cylinder 12 Misfire Detected
The P0312 code indicates that the engine control module (ECM) has detected a misfire in cylinder 12. A misfire occurs when the air-fuel mixture in the cylinder fails to ignite properly, causing a loss of power and increased emissions. This can be caused by issues with the ignition system, fuel delivery, or mechanical problems within the cylinder.
1. Most Common Causes
- Worn or damaged spark plug in cylinder 12
- Faulty spark plug wire or ignition coil
- Clogged or electrically faulty fuel injector
- Low compression in cylinder 12 (valves, piston rings, cylinder head)
- Incorrect air/fuel mixture (too lean or too rich)
- Vacuum leak in intake affecting cylinder 12
- Crankshaft position (CKP) sensor circuit issue or erratic signal
- Faulty idle air control (IAC) valve or throttle actuator
2. Symptoms You Will Notice
- Check Engine Light illuminated
- Engine runs rough or misfires, especially under load
- Reduced engine power and fuel economy
- Possible engine vibration or hesitation
3. Step-by-Step Diagnosis
Step 1: Scan for additional codes and freeze frame data to confirm P0312.
Step 2: Inspect spark plug and ignition coil on cylinder 12; swap with another cylinder to see if misfire follows.
Step 3: Check fuel injector on cylinder 12 for proper operation using a noid light or injector tester.
Step 4: Perform a compression test on cylinder 12 and compare to other cylinders.
Step 5: Inspect for vacuum leaks around intake manifold and hoses near cylinder 12.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive with a misfire as it can cause damage to the catalytic converter and other engine components. Have it diagnosed and repaired promptly.
How much does it cost to fix?▼
The cost varies depending on the cause. A spark plug replacement may cost $50-$150, while a fuel injector or ignition coil replacement can range from $150-$400 per part plus labor.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.