P0300: Random or Multiple Cylinder Misfire Detected
The engine is misfiring in more than one cylinder, or the computer cannot tell which one.
Severity: 3 of 4
Park it if the check engine light is flashing or the engine is shaking. A flashing light means misfires severe enough to damage the catalytic converter and in extreme cases cause an exhaust fire. If the light is steady and the misfire is mild, drive only as far as needed to get it diagnosed, gently and without heavy loads.
Estimate range covers the repairs listed below; see the cost breakdown. A flashing check engine light, a hot temperature gauge, or brakes that feel different mean stop driving and get help.
What P0300 means
The computer watches the speed of the crankshaft. Each time a cylinder fires it gives the crank a small push. When a cylinder fails to burn its fuel, that push is missing and the computer counts a misfire.
P0300 means the misfires are spread across several cylinders or are moving around. That points toward something shared by the whole engine, such as fuel pressure, a vacuum leak, or ignition parts that are all worn, rather than one bad coil.
Misfires dump raw fuel into the exhaust, which can overheat and ruin the catalytic converter quickly.
Common causes (cheapest likely first)
- Worn spark plugs. Plugs past their service interval misfire under load. Inexpensive and a common first step.
- Vacuum leak. A split hose or leaking intake gasket leans out every cylinder. Often seen with P0171 or P0174.
- Low fuel pressure. A weak pump, clogged filter, or bad regulator starves all cylinders.
- Bad ignition coil or plug wires. Usually causes a single cylinder code, but several weak coils can produce P0300.
- Dirty or failing fuel injectors. Clogged injectors spray poorly and misfire at random.
- Low compression or timing problem. A jumped timing chain or worn rings. Less common and more costly.
Symptoms
- Flashing or steady check engine light
- Rough idle or shaking
- Hesitation or stumbling on acceleration
- Loss of power
- Fuel smell from the exhaust
- Worse fuel economy
DIY difficulty: Moderate
Spark plugs and coils are often accessible on four cylinder engines. On many V6 engines the rear plugs require removing the intake plenum. Diagnosing fuel pressure or compression needs a gauge.
Tools: OBD-II scanner with misfire counters, Spark plug socket and extension, Torque wrench, Gap tool, Fuel pressure gauge for deeper diagnosis
Estimated repair cost
This is an estimate, built from typical parts price ranges plus labor hours times an assumed shop rate of $110 to $190 per hour. Actual prices vary by vehicle, region, and shop. Diagnosis fees are often extra.
| Repair | Parts | Labor | Estimate (low / high) |
|---|---|---|---|
| Spark plugs, full set | $20 to $120 | 0.5 to 2.5 h | $20 + 0.5 × $110 = $75 $120 + 2.5 × $190 = $595 |
| Vacuum hose or intake gasket | $10 to $120 | 0.5 to 2.5 h | $10 + 0.5 × $110 = $65 $120 + 2.5 × $190 = $595 |
| Ignition coil, one | $30 to $150 | 0.2 to 1.0 h | $30 + 0.2 × $110 = $52 $150 + 1.0 × $190 = $340 |
| Fuel pump | $120 to $600 | 1.5 to 3.5 h | $120 + 1.5 × $110 = $285 $600 + 3.5 × $190 = $1,265 |
Watch a repair video
How to Fix a Random Engine Misfire in Your Car (Code P0300) (Scotty Kilmer). Third-party video, loads from YouTube (privacy-enhanced mode) only when you press play. Procedures vary by vehicle. Search YouTube for “P0300 fix” videos.
P0300 by make
Brand specific notes: Ford, Chevrolet, GMC, Dodge, Ram, Honda, Subaru, Hyundai, BMW, Volkswagen. Other makes: the code works the same way; see all makes.
Repair manuals
Step-by-step service manuals with torque specs and wiring diagrams:
Haynes manuals Chilton manuals
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Related codes
Check for recalls
Before paying for a repair, enter your VIN in the NHTSA recall lookup. Emissions parts may also be covered by a federal emissions warranty; check your warranty booklet.
FAQ
Is it safe to drive with a P0300 code?
Only if the light is steady and the engine runs nearly normally, and only to get it fixed. If the light flashes, pull over safely and stop driving.
Can bad gas cause P0300?
Yes. Water or low quality fuel can cause random misfires. If the code appeared right after a fill up, that is a clue.
Will new spark plugs fix P0300?
If the plugs are overdue, often yes. If they are fresh, look for vacuum leaks or fuel delivery problems instead.