P0300: misfire on more than one cylinder

What the code means

A misfire happens when a cylinder does not burn its fuel properly. The code is P0300 and not P0301 to P0308, which means the pattern is random or spread out.

That usually points to something affecting the whole engine rather than one cylinder.

Common causes

• A vacuum leak, meaning unmetered air getting in
• A problem with the fuel supply
• Worn spark plugs across several cylinders at once
• Failing ignition coils

What to do now

1. Check whether the light is flashing. That sets the urgency, not the code.
2. If it is flashing, slow down. Unburnt fuel reaches the catalytic converter.
3. Note whether the engine shakes, loses power or idles roughly.
4. Have it read for additional codes stored at the same time. They often point at the cause.

What people often get wrong

Changing plugs and coils first, because it is the cheapest move. With P0300, a spread pattern, that is often the wrong place to start: a vacuum leak affects every cylinder equally, and new plugs change nothing.

When the car must go to a workshop

A flashing light with a misfire code should be checked immediately. A catalytic converter costs many times what spark plugs do.

Read next

• P0301 to P0308: a misfire on one specific cylinder
• P0171: system too lean
• Your check engine light isn't random

This page is general information and does not replace a professional assessment. Symbols, codes and behaviour vary between makes. Always check the handbook for your own car.