P0300 to P0316: engine misfire

What does P0300 mean?

Each cylinder speeds the crankshaft up a little when it fires. The engine computer watches those small accelerations through the crankshaft sensor, and when a cylinder fails to add its push often enough to raise emissions or overheat the catalytic converter, it stores a misfire code. A steady check engine light means the misfire is mild; a flashing light means it is bad enough to damage the converter right now.

What causes P0300?

1. Worn spark plugs, or a plug gap that has opened up with age
2. A failing ignition coil or plug lead: a single-cylinder code that moves when you swap coils points straight at it
3. A vacuum leak or a sticking injector that leaves one cylinder lean
4. Low fuel pressure or poor fuel, which tends to give P0300 rather than one cylinder
5. Mechanical trouble such as low compression, a burnt valve or a timing belt or chain that has slipped

What to check first for P0300

• Note whether the light flashes, and read every other code stored with it: a lean or sensor code often explains the misfire
• Check when the spark plugs were last changed against the service schedule
• On a single-cylinder code, swap that cylinder's coil with a neighbor's and see whether the code follows it
• Listen for hissing around the intake, the sound of a vacuum leak
• If plugs, coils and leaks are clear, have a compression test done

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