OBD Code P0300: Random Multiple Cylinder Misfire — Stop if Light is Flashing

What does code P0300 mean?

Code P0300 (Random/Multiple Cylinder Misfire Detected) means the ECU has detected misfires across multiple cylinders simultaneously — rather than one specific cylinder (which would be P0301, P0302, etc.).

⚠️ Flashing check engine light = stop driving immediately. Active misfires can destroy your catalytic converter in minutes. A solid light = you can drive carefully to a garage.

Symptoms of P0300

• Flashing or solid check engine light
• Engine vibration and rough running, especially at idle
• Hesitation and stumbling on acceleration
• Difficulty starting, especially cold
• Increased fuel consumption (15-25%)
• Exhaust smell of unburnt fuel

Common causes

1. Worn spark plugs (40% of cases)

Spark plugs should be replaced every 30,000-60,000 miles. A worn plug won't fire consistently. Always replace all plugs at the same time.

👉 NGK spark plugs on Amazon UK — match the exact part number for your vehicle

2. Faulty ignition coils (25%)

Modern engines use individual coil-on-plug coils. A failing coil causes persistent misfires on its cylinder. DIY test: swap coils between cylinders and clear the code. If the misfire follows the coil, replace it.

👉 Ignition coil on Amazon UK — £15-50 each

3. Clogged fuel injectors (15%)

A partially blocked injector doesn't deliver the right fuel quantity. Injector cleaner additive often resolves mild cases.

👉 Injector cleaner on Amazon UK — £8-12, add to a full tank

4. Compression issues (10%)

Head gasket, worn rings, or valve problems. If plugs and coils are fine and misfires persist, a compression test is the next step.

Diagnosis steps

1. Read all stored codes — companion codes P030X identify which cylinder
2. Swap coils/plugs between cylinders to localise the fault
3. Check for vacuum leaks on the intake manifold
4. Run a bottle of injector cleaner

👉 OBD2 scanner with live data on Amazon UK

Repair cost

Can I drive with P0300?

• Flashing light → NO. Stop immediately.
• Solid light → Cautiously, avoid high revs, drive to a garage same day.