OBD codes / P0300
P0300
SeriousRandom/Multiple Cylinder Misfire Detected
Treat P0300 with some urgency. A steady check-engine light with a mild misfire is usually drivable short-term, but a FLASHING light means raw fuel is reaching the catalytic converter and can ruin it — pull over and have it towed or diagnosed. Misfires also tend to get worse, so do not put the fix off.
What this code means
A misfire means one or more cylinders are not burning their air-fuel mixture properly — the engine briefly loses power on that cylinder and the computer detects the hiccup in crankshaft speed. P0300 means the misfires are random or spread across several cylinders rather than isolated to one. The most common culprits are worn spark plugs or failing ignition coils, but a vacuum (air) leak, a fuel-delivery problem, low compression, or a sensor feeding bad data can all cause it. Because unburned fuel can reach and overheat the catalytic converter, a steady misfire should not be left for long.
Symptoms you might notice
- Rough idle or noticeable shaking, especially when stopped
- Loss of power, hesitation, or stumbling under acceleration
- Flashing check-engine light during an active misfire
- Reduced fuel economy
- Hard starting or an engine that surges
What it costs to fix
Typical range: $100–$1,000 · about ~0.5–3 hrs of labor
| If the cause is… | Part | Labor |
|---|---|---|
| Spark plugs (full set) | $20–$120 | ~0.5–2 hrs |
| Ignition coil(s) | $30–$300 | ~0.5–1.5 hrs |
| Vacuum / intake leak repair | $20–$200 | ~0.5–2 hrs |
| Fuel injector | $100–$400 | ~1–3 hrs |
A plugs-and-coils fix is usually the low end; injectors, compression repairs, or a hard-to-reach coil on a V6/V8 push it higher. Labor climbs on engines where the intake or rear bank must come off to reach the parts.
The price swings on which cause it turns out to be — so confirm the cause before paying. Diagnose P0300 for my exact vehicle →
Frequently asked
Can I drive with P0300?
With a steady (not flashing) check-engine light and only a mild misfire, short trips are usually fine — but get it looked at soon. If the light is flashing, an active misfire is dumping raw fuel into the catalytic converter and can destroy it; stop driving and have the car towed.
Why is my check-engine light flashing with P0300?
A flashing light signals a severe misfire happening right now. The danger is unburned fuel overheating the catalytic converter, an expensive part. Ease off the throttle, pull over when safe, and get it diagnosed before driving further.
What is the most common cause of P0300?
Worn spark plugs and failing ignition coils are the most common, especially if the plugs are overdue. Vacuum (air) leaks are the next most common. Fuel and compression problems are possible but less frequent, which is why a proper diagnosis saves money.
How much does it cost to fix P0300?
Often modest — a set of spark plugs or a single coil is commonly a low-hundreds repair. It climbs if the cause is fuel injectors, low compression, or parts that are hard to reach on a V6 or V8. Confirm the cause before replacing parts in bulk.
Will P0300 clear itself?
If it was a one-off from bad fuel or moisture the light may eventually go out, but a real misfire almost always returns until the cause is fixed. Do not ignore a repeating P0300 — misfires tend to worsen and can damage the converter.
Seeing P0300 on your car? Get a diagnosis specific to your exact year, make and model.
Diagnose P0300 for my vehicleGeneric OBD-II reference. Manufacturer-specific behavior varies — confirm with a scan tool and, for safety-related codes, a professional inspection.