Error P0305 – how to fix it?

P0305 Code Definition

Cylinder fire fault detected 5

What does code P0305 mean?

P0305 is a generic OBD-II code that indicates that the engine control module (ECM) has detected an ignition error in cylinder number 5 of the engine.

What causes the P0305 code to occur?

• The spark plug will not ignite on cylinder #5 due to contamination or broken insulation.
• The ignition coil on cylinder #5 has stopped firing.
• The spark plug wire or plug cap has a spark leak to ground for cylinder number 5.
• The valve cover leaks oil into the spark plug holes and causes a short circuit when firing the spark plug for cylinder number 5.

What are the symptoms of code P0305?

• The Check Engine light will come on, and the code will be stored in the ECM memory.
• The Check Engine light may flash during a misfire, indicating that the catalytic converter may be damaged.
• The engine will not spark, causing knocking or pulling and idling.
• The engine may not have power during acceleration when the ignition error is active.

How can a mechanic diagnose a P0305 code?

• Scan the codes and document the freeze frame data to verify the problem.
• Clear the engine and ETC codes to see if the problem occurs again.
• Perform road tests to check for ignition failure on cylinder 5.
• Remove the cylinder 5 coil or spark plug wire and check for signs of spark on the outside of the coil or spark plug housing. Also look for oil contamination through a leaking valve cover.
• Remove and inspect the spark plug from the cylinder and replace it or change it to another cylinder to see if the misfire transfers to another cylinder.
• Check cylinder compression if no ignition problems are found.

The most common errors when diagnosing the P0305 code.

• Do not move the coil to another cylinder and rescan to see if the misfire moves to another cylinder to see if it is the coil that is bad.
• Do not replace a part with another cylinder to isolate the faulty part.

How serious is the code P0305?

An incorrectly ignited cylinder can cause the engine to run too rich and can damage the catalytic converter. An incorrect ignition will cause the engine to misfire and shut down when accelerating, resulting in reduced performance and fuel consumption.

What repairs can clear the P0305 code?

1. Replace the 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 faulty coil, spark plug wires and spark plugs.

Additional notes to consider about code P0305

The P0305 code is triggered when the crankshaft sensor does not receive crankshaft acceleration from the power stroke of cylinder number 5, meaning that this cylinder is not delivering power to the engine.