P0300: Random/Multiple Cylinder Misfire Detected
P0300 means the engine computer has detected misfires on more than one cylinder, or misfires that move around instead of staying on one cylinder. The most common fix is replacing worn spark plugs and checking ignition coils, with typical independent-shop repair costs of about $150 to $600 depending on what parts are needed.
- Severity
- High
- Can I drive?
- Drive with caution
- DIY?
- Possible with some experience
- Repair cost range
- $100 – $900
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What does P0300 mean?
P0300 sets when the PCM sees the engine running unevenly enough to count repeated misfires, but it cannot pin the problem to just one cylinder. A misfire happens when a cylinder does not burn the air-fuel mixture the way it should, which can shake the engine and reduce power. This code is often caused by ignition problems, fuel delivery issues, vacuum leaks, or an engine condition that is affecting several cylinders at once. Because the causes are broad, the same code can show up with a rough idle, hesitation, or a flashing check-engine light.
Common symptoms
- Check engine light on or flashing
- Rough idle
- Engine shaking or vibrating
- Hesitation when accelerating
- Loss of power
- Bad fuel economy
Causes, fixes and costs
P0300: Random/Multiple Cylinder Misfire Detected
General guide for most cars. Your car may differ.
A persistent misfire can damage the catalytic converter and may leave you with poor power or stalling. Stop driving if the check-engine light is flashing hard, the engine is shaking severely, or the car will not accelerate normally.
Most likely causes
- 1
Worn spark plugsHigh
A worn or fouled plug often causes rough idle, hesitation, and misfires under load. This is especially likely if the plugs are overdue or the engine has high mileage.
Quick check: Inspect the spark plugs for wear, heavy deposits, oil fouling, or wide electrode gaps.
- 2
Weak or failing ignition coilsHigh
Bad coils often cause misfires that come and go, shaky idle, or a flashing check-engine light. The problem may be worse when the engine is under load or in damp weather.
Quick check: Scan for cylinder misfire counts and swap coils between cylinders if the engine design allows it.
- 3
Vacuum leakMedium
A vacuum leak can make the mixture too lean, causing multiple-cylinder misfires, rough idle, and sometimes a hissing sound. It is more likely if the engine idles worse than it does at higher RPM.
Quick check: Listen for hissing and inspect intake hoses, PCV hoses, and the brake booster line for cracks or loose fittings.
- 4
Fuel delivery problemMedium
Low fuel pressure or dirty injectors can cause hesitation, power loss, and misfires across several cylinders. This is more likely if the car struggles under acceleration or the issue gets worse when fuel demand is high.
Quick check: Check fuel pressure and injector performance; a pressure test can confirm whether the fuel system is meeting spec.
Can you fix it yourself?
Possible with some experience
Difficulty: Moderate. Basic tune-up checks like spark plugs, coil inspection, and hose inspection can be DIY work on many cars. If the problem needs fuel pressure testing, injector diagnosis, or deeper engine diagnostics, a shop is the better choice.
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- Scan for stored codes and freeze-frame data
- Check whether the misfire is constant or only under load
- Inspect spark plugs and coils for wear or damage
- Look for cracked vacuum hoses or loose intake parts
- Check for obvious vacuum leaks and air intake issues
- Verify fuel quality and fuel filter condition if equipped
- Clear codes and retest after repairs
Estimated repair cost
$120 – $350
Spark plugs: parts and labor; depends on engine access
- Ignition coils$180 – $600
- Vacuum leak repair$100 – $450
- Fuel injector cleaning or replacement$150 – $900
- Fuel pressure diagnosis and repair$120 – $700
Prices vary by vehicle, engine layout, and local labor rates.
Frequently asked questions
Can I drive with code P0300?
You may be able to drive a short distance if the engine is running fairly smooth and the light is solid, but you should get it checked soon. If the light is flashing or the engine is shaking badly, stop driving and have it towed.
Will P0300 clear itself?
Sometimes the light may turn off if the misfire stops, but the underlying problem usually does not fix itself. If the cause is still there, the code will come back.
Is P0300 usually spark plugs or coils?
Very often, yes. Worn spark plugs and weak ignition coils are among the most common causes, but vacuum leaks and fuel system problems are also possible.
Can P0300 fail an emissions test?
Yes. A misfire code can cause an emissions failure, and some states will also fail the car if the check-engine light is on or if readiness monitors are not complete.
Do I need a mechanic for P0300?
Not always. If you can inspect plugs, coils, and hoses safely, you may find the cause yourself, but a shop is usually needed if the misfire is random, intermittent, or still present after basic checks.
Related codes
Related problems
This guide covers most cars and is general advice, not an inspection. Prices are typical US independent-shop ranges and vary by region, car and shop. If your brakes, steering or a warning light feel unsafe, stop driving and contact a mechanic.