P0300 Code: Random or Multiple Cylinder Misfire Detected
P0300 means the engine computer detected misfires on several cylinders or at random, rather than on one specific cylinder. Because several cylinders are affected, the cause is usually something they share: worn spark plugs, a vacuum leak, low fuel pressure, a dirty mass air flow sensor or, less often, a mechanical problem.
P0300 vs. P0301–P0308
Codes P0301 to P0308 name a single cylinder (P0302 is cylinder 2, for example). That points to a part on that cylinder, such as one ignition coil or injector. P0300 means the misfires move around or affect several cylinders, so look for a cause common to the whole engine. P0300 often appears together with one or more cylinder-specific codes.
Symptoms
- Rough idle or shaking at stops
- Hesitation, stumbling or jerking when accelerating
- Check engine light, which may flash during heavy misfiring
- Loss of power and worse fuel economy
- Fuel smell from the exhaust
Most common causes
| Cause | Clues |
|---|---|
| Worn spark plugs | Past the service interval; misfire worse under load |
| Vacuum leak | Lean codes P0171/P0174 too; hissing sound; worse at idle |
| Dirty or failing mass air flow sensor | Lean codes, hesitation; often improves after cleaning |
| Low fuel pressure | Misfire under load or at high speed; lean codes |
| Failing ignition coils (several) | Cylinder-specific codes alongside P0300 |
| Bad fuel or water in fuel | Started right after a fill-up |
| Mechanical problem (low compression, timing) | Persistent misfire, ticking or rattling, timing codes |
How to track down the cause
- Read freeze-frame data: was the engine cold, idling or under load when it misfired?
- Check for other codes, especially lean codes and cylinder-specific misfires
- Inspect spark plugs: worn, oily or carbon-fouled plugs explain a lot
- Listen and smoke-test for vacuum leaks
- Check fuel trims and fuel pressure
- Run a compression test if the basics check out
Is it safe to drive?
With a steady check engine light and a mild misfire, drive gently to a shop. If the light is flashing, misfires are severe enough to overheat the catalytic converter: reduce load and get the car checked as soon as possible.
Frequently asked questions
Can a bad battery cause P0300?
Rarely. Very low system voltage can cause erratic ignition, but plugs, vacuum leaks and fuel delivery are far more common causes.
Will new spark plugs fix P0300?
Often, if the plugs are worn or past their interval. If they are fairly new, look at vacuum leaks, fuel pressure and the MAF sensor next.
Can P0300 damage the engine?
Prolonged misfiring can damage the catalytic converter and, over time, wash oil off cylinder walls. Fix it promptly.
Related repair costs
More guides
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- Why Does My Car Shake When Braking?
- How Long Do Brakes Last?
Sources and methodology
Estimates combine typical book labor times, current aftermarket and OEM parts prices, and 2026 US shop labor rates. See exactly how we calculate them.
- U.S. Bureau of Labor Statistics: Occupational Employment and Wage Statistics, automotive service technicians (49-3023), by state
- U.S. Bureau of Labor Statistics: Automotive Service Technicians and Mechanics (pay and duties)
- Federal Trade Commission: Auto Repair Basics (estimates, warranties, your rights)
- NHTSA: Check for recalls before paying for a repair (our free recall check uses NHTSA data)
- ASE (National Institute for Automotive Service Excellence): technician certification