P0300 Code: Random/Multiple Cylinder Misfire Detected

The P0300 trouble code is set when the engine computer detects misfires occurring randomly or across multiple cylinders. Misfires can cause rough running, loss of power, and can quickly damage the catalytic converter if ignored.

Ignition + Fuel + Air Catalyst Risk Common Code Often w/ P0171/P0174
On this page
  1. What P0300 Means
  2. Symptoms
  3. Common Causes
  4. Is P0300 Serious?
  5. How to Diagnose P0300
  6. How to Fix P0300
  7. Repair Cost Estimates
  8. FAQs

What Does P0300 Mean?

Code
P0300
Definition
Random/Multiple Cylinder Misfire Detected
System
Ignition / Fuel / Air (Combustion)
Severity
High (risk of catalytic converter damage)
Related Codes
P0301–P0308, P0171, P0174, P0101

A misfire happens when one or more cylinders do not burn the air-fuel mixture correctly. Unlike cylinder-specific codes (such as P0301 for cylinder 1), P0300 indicates misfires that are random or happening in multiple cylinders.

Symptoms of P0300

  • Rough idle and engine shaking
  • Loss of power / poor acceleration
  • Hesitation or stumbling under load
  • Hard starting
  • Stalling at idle
  • Strong fuel smell from exhaust (sometimes)
  • Check Engine Light (CEL) on or flashing
Flashing CEL: A flashing Check Engine Light often indicates an active misfire severe enough to damage the catalytic converter.

Common Causes of P0300

Ignition System Problems

  • Worn or fouled spark plugs
  • Failing ignition coils
  • Damaged plug wires (if equipped)
  • Moisture/oil in plug wells (common on some engines)

Fuel Delivery Issues

  • Weak fuel pump
  • Low fuel pressure
  • Dirty or clogged fuel injectors
  • Fuel contamination or incorrect fuel

Air/Fuel Mixture Problems

  • Vacuum leaks
  • Dirty or faulty MAF sensor
  • EVAP purge valve stuck open
  • Exhaust leak affecting O2 sensor readings

Sensor / Control Issues

  • Crankshaft position sensor problems
  • Camshaft position sensor problems
  • Throttle body or MAP sensor issues (if equipped)

Mechanical Problems

  • Low compression
  • Timing chain/belt issues
  • Valve problems (burnt/sticking valves)
  • Head gasket issues (less common, but possible)

Is the P0300 Code Serious?

Yes. Misfires can send unburned fuel into the exhaust, overheating and damaging the catalytic converter. Continued misfires can also lead to poor drivability and, in severe cases, engine damage.

How to Diagnose P0300

  1. Scan for additional codes (P0301–P0308 can identify cylinders; P0171/P0174 and P0101 point to mixture/MAF issues).
  2. Review freeze-frame data to see RPM/load/temperature when the misfire was detected.
  3. Inspect spark plugs for wear, gap issues, oil fouling, or carbon buildup.
  4. Test ignition coils and look for cracks, arcing marks, or weak output.
  5. Check fuel trims (lean conditions can trigger random misfires).
  6. Verify fuel pressure under load if symptoms worsen during acceleration.
  7. Inspect intake/vacuum hoses for leaks and loose connections.
  8. Check MAF readings and clean the MAF sensor if readings are erratic.
  9. Compression test if misfires persist after ignition/fuel checks.

How to Fix P0300 (Most Effective Repairs)

Repair When it makes sense
Replace spark plugs Plugs are worn, fouled, or overdue
Replace ignition coils Weak spark, misfire moves with coil swap, or multiple coil failures
Fix vacuum leaks Lean fuel trims, rough idle, smoke test confirms leaks
Clean/replace the MAF sensor MAF data inconsistent, P0101 present, lean/misfire combination
Fuel injector cleaning/service Misfires under load, injector balance concerns, restricted injector suspected
Correct fuel pressure issues Low pressure readings, symptoms worsen with acceleration
Mechanical repair (compression/timing/valves) Compression low, persistent misfire after ignition/fuel/air checks

P0300 Repair Cost Estimates

Repair Estimated Cost
Spark plug replacement$50 – $250
Ignition coil replacement$80 – $450
MAF cleaning$10 – $25
MAF replacement$80 – $350+
Vacuum leak repair$50 – $250
Fuel injector cleaning$80 – $200
Fuel injector replacement$150 – $600
Fuel pump replacement$350 – $1,000+

FAQs

What’s the difference between P0300 and P0301?

P0300 indicates random or multiple cylinder misfires. P0301 indicates a misfire in cylinder 1 specifically.

Can a vacuum leak cause P0300?

Yes. Vacuum leaks can create a lean condition that leads to random misfires, especially at idle or light throttle.

Can P0300 damage the catalytic converter?

Yes. Misfires can send unburned fuel into the exhaust, overheating the catalytic converter and causing costly damage.

Related pages:
P-Codes Hub • P0171 (Lean Bank 1) • P0174 (Lean Bank 2) • P0101 (MAF Range/Performance) • Code Library (Search)