P0300: Random or Multiple Cylinder Misfire Detected
Applies to: Universal OBD-II (Ford, Chevy, Toyota, Honda, BMW)
Can you still drive / use device? No. Driving with a flashing check engine light causes irreversible catalytic converter damage.
Common Symptoms
- Flashing Check Engine Light (CEL)
- Engine shaking, vibrating, or jerking at idle
- Noticeable loss of engine power when accelerating
- Strong gasoline smell from exhaust or poor fuel economy
- Stumbling or stalling at stoplights
Root Causes
- Worn or fouled spark plugs and damaged spark plug wires
- Failing ignition coils or coil packs
- Clogged fuel injectors or low fuel rail pressure
- Intake manifold vacuum leak
- Low engine compression or faulty Camshaft/Crankshaft sensor
Step-by-Step Instructions to Fix P0300
Scan with OBD-II Scanner for Accompanying Codes
Plug a handheld OBD-II scanner into the 16-pin port under the dashboard. Check if specific cylinder codes like P0301 (Cylinder 1) or P0304 (Cylinder 4) accompany P0300.
Inspect and Replace Spark Plugs
Remove the ignition coils, use a spark plug socket with ratchet to unthread spark plugs. Inspect electrode tips for carbon buildup, oil fouling, or burnt gaps. Replace with OEM iridium plugs gapped to spec.
Test Ignition Coils
Perform an ignition swap test: Swap coil from a suspected misfiring cylinder to an adjacent cylinder. Clear codes and re-scan. If the misfire moves, replace the faulty coil.
Check for Vacuum Leaks
Inspect PCV hoses, intake boot, and vacuum lines for cracking or hissing sounds while engine idles. Smoke test the intake if necessary.
Verify Fuel Delivery and Clear DTC Codes
Add a bottle of premium fuel injector cleaner (e.g. Chevron Techron). Clear the OBD-II codes with your scanner and take the car on a 15-minute drive cycle to confirm readiness monitors reset.
How to Prevent P0300 in the Future
- Replace spark plugs every 60,000 to 100,000 miles according to manufacturer schedule.
- Never ignore a steady Check Engine light before it begins to flash.
- Use Top Tier detergent gasoline to prevent carbon buildup on valves and injectors.