P0300: Random/Multiple Cylinder Misfire Detected

Common causes

• Worn spark plugs
• Failing ignition coils or plug wires
• Vacuum leaks or a lean condition
• Clogged or leaking fuel injectors
• Low compression (less common)

Code meanings can vary slightly by manufacturer. Use these as a starting point and confirm with your vehicle's service information or a mechanic before replacing parts.

Symptoms

• Shaking or rough running, especially at idle
• Loss of power and poor fuel economy
• A flashing check engine light during severe misfires

Is it safe to drive?

If the check engine light is flashing, stop driving as soon as it's safe: severe misfires can overheat and ruin the catalytic converter quickly and can cause sudden power loss. Have it towed, or drive only a very short distance gently. With a steady light, get it checked soon.

How to check it with a scanner

1. Plug an OBD2 scanner into the port under the dashboard and read all stored codes and the freeze-frame data (the conditions when the code set).
2. Read misfire counts per cylinder in live data (many scanners show this) to see which cylinders are affected.
3. Check for lean codes (P0171/P0174) at the same time.
4. Inspect spark plugs, and swap a suspect coil to another cylinder to see if the misfire follows it.
5. After a repair, clear the code and drive normally for a few days to confirm it doesn't come back.

A basic code reader shows the code; scanners with live data let you watch sensor readings, which is what you need for most of the checks above. See OBD2 scanners under $100.

Questions

Related codes

• P0171: Engine running lean, bank 1
• P0420: Catalytic converter efficiency, bank 1
• P0011: Intake cam timing over-advanced, bank 1
• All trouble codes
• How to choose a car diagnostic scanner