Error P0305 – how to fix?

P0305 Code Definition

Cylinder 5 fire failure detected

What does the code P0305 mean?

P0305 is the general OBD-II code which indicates that the engine control module (ECM) has detected a misfire on engine cylinder number 5.

What causes the code P0305?

• Spark plug does not ignite in cylinder # 5 due to dirt or crack in the insulation.
• Cylinder number 5 ignition coil stopped firing.
• The spark plug wire or spark plug shroud has a spark plug leak to ground for cylinder number 5.
• Oil leaks from the valve cover into the spark plug holes and causes a spark plug short circuit for cylinder number 5.

What are the symptoms of the P0305 code?

• The Check Engine light will come on and the code will be stored in the ECM’s memory.
• The Check Engine light may flash during a misfire, indicating that the catalytic converter may be damaged.
• The engine will not fire, causing knocking or pulling and rough idling.
• The engine may have no power during acceleration while the ignition fault is active.

How can a mechanic diagnose the P0305 code?

• Scan the codes and document the data from the frozen frame to verify the problem.
• Clears engine codes and ETCs to see if the problem recurs.
• Make road tests to check that there is no ignition in cylinder 5.
• Remove cylinder 5 ignition coil or spark plug wire and inspect the outside of the coil or spark plug housing for signs of a spark. You should also pay attention to contamination of the oil through a leaky valve cover.
• Remove and inspect the spark plug from the cylinder and replace it or change to a different cylinder to see if the misfire is transferring to another cylinder.
• Check cylinder compression if no ignition problems are found.

The most common errors when diagnosing the code P0305

• Do not change the coil to another cylinder and scan again to see if the misfire is transferring to the other cylinder to see if that coil is bad.
• Do not replace one part with another cylinder to isolate the damaged part.

How serious is the P0305 code?

An improperly lit cylinder can cause the engine to run too richly and can damage the catalytic converter. If the ignition is not correct, the engine will not start and will hang when accelerating, which will reduce performance and fuel consumption.

What repairs can remove the P0305 code?

1. Replace faulty spark plug, or replace all spark plugs together if the cause of the fault is a worn spark plug.
2. Replace the leaking valve cover gasket, then replace the damaged coil, spark plug wires, and spark plugs.

Additional considerations for code P0305

Code P0305 triggers when the crankshaft sensor is not receiving crankshaft acceleration from the power stroke of cylinder number 5, indicating that this cylinder is not supplying power to the engine.