P0300Ignition and misfires

P0300: Random/Multiple Cylinder Misfire Detected

P0300 means the engine computer detected misfires (a cylinder failing to fire properly) that it could not pin on one cylinder. A steady check engine light means get it checked soon, but a flashing light means a misfire rate high enough to damage the catalytic converter, so stop driving as soon as it is safe.

You can drive, but get it checked soon

With a steady light and mild symptoms, a short drive to a shop is generally acceptable. If the light is flashing, the misfire is at a catalyst-damaging rate, so reduce load, avoid hard acceleration and stop driving as soon as it is safe. The vehicle may also enter limp mode (reduced power).

What it means

The engine computer watches crankshaft speed. A cylinder that does not fire gives no acceleration push, and the computer notices the dip. P0300 sets when the misfires cannot be assigned to a single cylinder: several cylinders each account for a significant share, the misfiring cylinder keeps changing, or (on Ford) the cylinder cannot be identified at high engine speed. The light turns on after two trips when the misfire rate affects emissions, and it flashes when the rate is high enough to damage the catalytic converter, the exhaust part that cleans the fumes. Some Ford and GM vehicles may shut off the fuel injector of a misfiring cylinder to protect the catalyst. Because several cylinders are involved, the cause is usually something that affects the whole engine, such as an air leak, worn spark plugs, or fuel problems. P0300 often shows up together with single-cylinder codes.

Likely causes

False air (vacuum leak, crankcase ventilation, intake gasket)Very likely
Unmetered air leaking in makes the fuel mixture too lean, which can cause misfires across several cylinders.
Worn or wrong spark plugs on several cylinders, or faulty ignition coilsVery likely
Old or incorrect plugs and weak coils produce a poor spark; service bulletins also name cracked plug insulators and wrong plug gaps.
Fuel pressure too low or too high, or contaminated fuelPossible
Incorrect pressure or bad fuel upsets combustion in all cylinders at once.
Valve timing, valves or compression problems on several cylindersLess likely
A stretched timing chain or worn valves change when and how well cylinders breathe and burn.
False detection (damaged tone wheel or pulley, rough road, vibration, software)Less likely
The computer reads crankshaft speed, so a damaged signal wheel or a bumpy road can look like a misfire.

What you may notice

Check engine light on, flashing at a catalyst-damaging rate
Rough idle, jerking, vibration
Loss of power, hesitation
Smell of unburnt fuel, higher fuel consumption

What to check, cheapest first

1Note whether the check engine light is steady or flashing, and when the problem happens (cold start, idle, under load, rough road). · you can do it
2Read all stored codes. Cylinder-specific codes such as P0301 or P0302, or fuel trim codes such as P0171, point to where to look first. · you can do it
3Look and listen for air leaks: cracked or disconnected vacuum hoses, crankcase ventilation hoses and the intake area, often shown by hissing or a high idle. · you can do it
4Inspect the spark plugs and ignition coils. Check plug condition, gap and type, and replace worn plugs as a set. · you can do it
5Test fuel pressure and consider the quality of the last fuel fill. · mechanic
6Check the crankshaft tone wheel or pulley, valve timing and cylinder compression if the simpler causes are ruled out. · mechanic

Frequently asked questions

Can I drive with a P0300 code?+

Only carefully and briefly if the light is steady. If it flashes, stop as soon as it is safe, because the misfire can damage the catalytic converter.

Can a loose gas cap cause P0300?+

The data does not list the gas cap as a cause. A loose cap usually triggers an evaporative system code instead, so look at air leaks, plugs, coils and fuel first.

Will P0300 pass an emissions test?+

Unlikely. The code is emissions-relevant and turns the check engine light on. After repair, the vehicle needs a drive cycle (a set of normal driving conditions) so the computer can confirm the fix.

Can I fix P0300 myself?+

Often, yes. Repair difficulty is medium and DIY is possible, with an estimated 0.5 to 6 hours depending on the cause. Spark plugs, coils and hoses are the usual starting points.

Written with the help of AI from the public OBDex definition (CC0). Each make may use the code differently. Updated: 2026-11-10