Quick answer: Code P0300 means “Random/Multiple Cylinder Misfire Detected”: the engine computer has detected misfires that aren’t limited to one cylinder. Most fixes are inexpensive, such as spark plugs ($100–$300), ignition coils ($150–$500) or a vacuum leak ($100–$400), but it can also point to fuel delivery or internal engine problems costing $1,000 or more.
What P0300 means
A misfire happens when the air-fuel mixture in a cylinder doesn’t burn properly. Codes P0301–P0308 point to a specific cylinder; P0300 means misfires are happening in several cylinders or randomly, which usually points to something that affects the whole engine.
Common causes and repair costs
Typical independent shop prices, October 2026.
| Cause | Clues | Typical repair cost |
|---|---|---|
| Worn spark plugs | Due by mileage (often 60,000–100,000 mi) | $100 – $300 (4-cyl), $250 – $600 (V6) |
| Failing ignition coils | Often also a cylinder-specific code | $150 – $500 |
| Vacuum leak | Lean codes P0171/P0174, hissing | $100 – $400 |
| Dirty or failing fuel injectors | Rough idle, poor fuel economy | $150 – $1,000 |
| Low fuel pressure (pump, filter, regulator) | Misfires under load | $300 – $1,200 |
| Dirty or faulty MAF sensor | Hesitation, lean codes | $20 (cleaning) – $350 |
| Carbon buildup (direct-injection engines) | High-mileage GDI engines | $300 – $800 (walnut blasting) |
| Low compression (valves, rings, head gasket) | Failed compression test | $1,500+ |
See plug prices in Spark Plug Replacement Cost and engine repairs in Head Gasket Replacement Cost.
On V8 pickups, misfires with a ticking noise can point to failed lifters: see Chevy Silverado 5.3L Lifter Replacement Cost and Ram 1500 HEMI Lifter and Camshaft Replacement Cost.
Symptoms that come with P0300
- Rough idle or shaking at a stop.
- Hesitation or stumbling when accelerating.
- Loss of power and worse fuel economy.
- Flashing check engine light: a severe misfire.
Is it safe to drive with P0300?
If the check engine light is flashing, stop driving as soon as it’s safe. Severe misfires send unburned fuel into the exhaust and can overheat and destroy the catalytic converter, a $600–$2,500 repair (see Catalytic Converter Replacement Cost). If the light is steady and the car runs normally, get it checked soon.
How a shop diagnoses P0300
- Reads misfire counters per cylinder and checks freeze-frame data.
- Inspects spark plugs and coils and swaps coils between cylinders to see if the misfire follows.
- Checks fuel trims and smoke-tests for vacuum leaks.
- Tests fuel pressure and injector operation.
- Runs a compression or leak-down test if the basics check out.
Diagnosis typically costs $100–$200, often credited toward the repair.
Frequently asked questions
Can bad gas cause P0300?
Yes, contaminated or very low-quality fuel can cause random misfires. It’s less common than worn plugs or coils.
Will new spark plugs fix P0300?
Often, if the plugs are old. If the code returns, look at coils, vacuum leaks and fuel delivery.