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P0306 OBD-II Trouble Code: Cylinder 6 Misfire Detected

Check Engine Light

P0306 code definition

Cylinder 6 Misfire Detected

What the P0306 code means

P0306 is an OBD-II generic code that the engine control module (ECM) detected a misfire on cylinder number 6 of the engine.

What causes the P0306 code?

  • The spark plug is not firing for cylinder number 6 due to fouling or cracks in the insulation.

  • The ignition coil for cylinder number 6 has stopped firing due to cracked insulation or open circuit.

  • The spark plug wire or plug boot is leaking ignition spark to ground for cylinder number 6 from age.

  • The valve cover is leaking oil into the spark plug holes and shorting the spark plug ignition for the number 6 cylinder.

  • The cylinder has problems with compression being low from defective rings or valves.

What are the symptoms of the P0306 code?

  • The Check Engine Light will be illuminated and the code is set in ECM memory.
  • The Check Engine Light will flash during a misfire event.
  • The engine will have a misfire and may buck or jerk on acceleration.
  • The engine will lack power during acceleration while the misfire is active and may affect transmission shifting.

How does a mechanic diagnose the P0306 code?

  • Scans codes and documents the freeze frame data in order to verify the problem.
  • Clears the engine and ETC codes and road test to verify concern comes back.
  • Removes cylinder 6 ignition coil or plug wire and checks for evidence of spark tracking on outside of coil or plug boot. Also look for oil contamination from a leaking valve cover.
  • Removes the cylinder number 6 spark plug for inspection and makes replacement if necessary.
  • Check engine cylinders compression if no ignition problems are found.

Common mistakes when diagnosing the P0306 code

  • Not switching the coil to a different cylinder to see if the misfire moves to another cylinder. This would indicate a bad coil.

  • Not switching one part at a time with a different cylinder to isolate the failed part.

How serious is the P0306 code?

  • A misfiring cylinder can cause the engine to run excessively rich and can damage the catalyst.
  • The misfire will cause the engine to run rough and hesitate on acceleration.
  • The engine will use more fuel due to the misfire.

What repairs can fix the P0306 code?

  • Replace the faulty spark plug or replace all spark plugs as a set if failure was due to a worn out plug.

  • Replace the leaking valve cover gasket then replace the failed coil, plug wires, and plugs.

  • Replace the ECM for a bad circuit that powers the fuel injector or coil for number 6.

Additional comments for consideration regarding the P0306 code

Code P0306 is triggered when the crankshaft sensor does not get an acceleration of the crankshaft from cylinder number 6 firing properly indicating the cylinder is not contributing to the engine power.

Need help with a P0306 code?

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The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
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