P0300
Random/Multiple Cylinder Misfire Detected
high
i Description
The ECU has detected misfires occurring in multiple cylinders with no single cylinder dominating. This is often caused by something common to all cylinders, such as fuel pressure, ignition timing, vacuum leaks, or EGR issues.
? Common Causes
- Worn spark plugs
- Low fuel pressure
- Large vacuum leak
- EGR valve stuck open
- Ignition timing fault
- Low compression across multiple cylinders
- Bad fuel
! Symptoms
- Check engine light (often flashing)
- Rough idle and vibration
- Loss of power
- Hesitation and stumble
- Failed emissions test
- Possible catalytic converter damage
# Diagnostic Steps
- Check for cylinder-specific misfire codes (P0301-P0312)
- Inspect spark plugs and ignition coils
- Test fuel pressure
- Check for vacuum leaks
- Test EGR valve operation
- Perform compression test
- Try a tank of premium fuel to rule out bad fuel
⚙ Typical Fix
Replace spark plugs and leads, repair vacuum leaks, or fix fuel delivery issues.
Parts Needed
Spark plugs, Ignition leads/coils, Fuel filter
Estimated Cost
$100-$600
↔ Related Codes
Q Frequently Asked Questions
If the check engine light is flashing, stop driving immediately — a flashing light means severe misfires that can destroy the catalytic converter. If the light is steady, drive carefully to a mechanic.
If it is spark plugs, yes — a basic tune-up is a common DIY job. For vacuum leaks or fuel pressure issues, more diagnosis is needed.
Spark plugs: $40-$120 for a set. Ignition coils: $40-$100 each. Fuel pump: $300-$600. Vacuum leak repair: $100-$300.
☞ Learn More
- What is OBD-II? — Complete guide to your car's diagnostic system
- How to Read DTC Codes — Step-by-step with a Bluetooth scanner
- OBD-II Scanner Buying Guide — Find the best scanner for your car