Cylinder 12 Misfire Detected
Diagnostic trouble code P0312 indicates that the powertrain control module (PCM) has detected a misfire in cylinder number 12. The PCM monitors the crankshaft position sensor for rotational speed variations, and sets this code when the crankshaft speed drops during cylinder 12's power stroke.
A misfire can cause significant drivability issues and lead to severe catalytic converter damage if left unaddressed. If the check engine light is flashing, stop driving immediately to prevent expensive damage.
Common symptoms
- Check engine light illuminated or flashing
- Rough idle or engine hesitation
- Noticeable lack of engine power
- Poor fuel economy
- Smell of unburned fuel from the exhaust
Likely causes
- Faulty spark plug in cylinder 12
- Defective ignition coil for cylinder 12
- Clogged or failing fuel injector on cylinder 12
- Vacuum leak affecting cylinder 12
- Low engine compression in cylinder 12
- Wiring or connector issues in the ignition or fuel injector circuits for cylinder 12
What to check before replacing parts
Scan for other codes and check freeze frame data.
Look for: Look for lean/rich codes or multiple cylinder misfires which might indicate a broader issue rather than a single cylinder problem.
Inspect the ignition coil and spark plug for cylinder 12.
Look for: Check for physical damage, carbon tracking, oil or coolant contamination in the spark plug well, and verify the spark plug gap and condition.
Swap the ignition coil from cylinder 12 to another cylinder.
Look for: Clear the codes and run the engine. If the misfire code moves to the new cylinder (e.g., P0311 for cylinder 11), the ignition coil is faulty.
Test the fuel injector for cylinder 12.
Look for: Listen for a clicking sound using a stethoscope to confirm operation, and check the injector's resistance with a multimeter to ensure it is within factory specifications.
Perform a compression test on cylinder 12.
Look for: Compare the compression reading of cylinder 12 to the other cylinders. A significantly lower reading indicates a mechanical issue such as a burnt valve, blown head gasket, or worn piston rings.
This page explains the generic P0312 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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