OBD code P0300

The ECU has detected combustion misfires across multiple cylinders or at random. If it continues, it can damage the catalytic converter.

Estimated severity

High

Common symptoms

Rough idle or clear engine vibration
Jerking under acceleration and noticeable power loss
Higher fuel consumption and a heavy engine feel
Check engine light steady or flashing
Smell of unburned fuel from the exhaust in severe cases

Likely causes

Worn, fouled or incorrect spark plugs
Faulty ignition coils or poor coil connections
Damaged spark plug wires or corroded connectors
Dirty, partially blocked or leaking injectors
Vacuum leaks in the intake system affecting the mixture
Low compression in one or more cylinders due to internal wear

Recommended checks

1. Read all fault codes and freeze-frame data such as rpm, load and affected cylinders.
2. Inspect the spark plugs and replace them if worn, dirty or incorrect for the engine.
3. Check the ignition coils by swapping them between cylinders and seeing whether the misfire moves.
4. Inspect ignition and injection connectors and wiring for poor contacts.
5. Look for vacuum leaks in intake hoses, brake booster lines, crankcase ventilation and related areas.
6. If the issue remains, perform a compression test or cylinder leak-down test.

What does code P0300 mean?

Code P0300 means one or more cylinders are misfiring intermittently. The air-fuel mixture is not burning correctly, and unburned fuel can reach the exhaust, overheating the catalytic converter and increasing emissions. It is one of the most common OBD codes and is often linked to ignition, fuel injection or internal engine wear.

Try assisted diagnostics