P0306 — Cylinder 6 Misfire Detected

Quick Answer

• What it means: The engine control module (ECM) has detected a misfire in cylinder 6.
• Severity: Moderate to severe; continued driving can damage the catalytic converter or other engine components.
• Most common cause: Faulty spark plug or ignition coil for cylinder 6.

What the P0306 code means

The P0306 code stands for "Cylinder 6 Misfire Detected." This means that the engine's computer (ECM/PCM) has detected that cylinder number 6 is not contributing power to the engine as expected. This can happen when the combustion process in that cylinder is incomplete or absent. The ECM monitors the crankshaft speed and acceleration, and if it detects an irregularity that correlates with the firing of cylinder 6, it will set this code.

In plain English, your engine isn't running smoothly because one of its cylinders, specifically cylinder 6, isn't firing correctly. Think of it like trying to row a boat with one oar missing or bent – you're not going to go straight or as fast.

Common symptoms

• Check Engine Light illuminated (often flashing for severe misfires)
• Rough idling or vibrations
• Reduced engine power or acceleration
• Poor fuel economy
• Engine hesitation or stumbling
• A strong smell of raw fuel from the exhaust
• Engine knocking or pinging sounds under load

Common causes (ranked from most to least likely)

1. Faulty Spark Plug or Ignition Coil: A worn, fouled, or damaged spark plug, or a failing ignition coil, is the most common culprit. These components are crucial for igniting the air-fuel mixture.
2. Ignition System Issues: Worn or damaged spark plug wires (if applicable) or a failing distributor cap and rotor (on older vehicles) can also lead to misfires.
3. Fuel Delivery Problems:
   • Clogged Fuel Injector: A faulty or dirty fuel injector for cylinder 6 can fail to deliver enough fuel, or any fuel at all, causing a lean misfire.
   • Low Fuel Pressure: Issues with the fuel pump or fuel pressure regulator can lead to insufficient fuel delivery to all cylinders, but may manifest as a misfire in one particularly sensitive cylinder first.
4. Compression Issues:
   • Worn Piston Rings: Loss of compression due to worn piston rings can prevent proper combustion.
   • Burnt or Leaking Valves: Valves that don