P0300 Code: Random/Multiple Cylinder Misfire Detected

What does P0300 mean?

Every time a cylinder fires, it gives the crankshaft a small push. When a cylinder fails to burn its fuel, that push is missing and the crankshaft slows for an instant. The engine computer watches crankshaft speed through the crankshaft position sensor and counts those dips as misfires ^[3].

California's OBD II regulation requires the system to watch for misfire and to identify the cylinder that is misfiring. When more than one cylinder is misfiring, it must store a separate code that says multiple cylinders are misfiring, and if two or more cylinders each cause more than 10 percent of the counted misfires, that multiple cylinder code is required ^[1]. That code is P0300.

P0300 does not mean the computer is confused. It means the misfires are spread out, which points you toward problems the cylinders share. You will often see it next to one or more cylinder codes, such as P0301 for cylinder 1. Those extra codes are useful because they tell you where to look first.

Is it safe to drive with P0300?

No. Treat P0300 as a stop driving code, and treat a flashing check engine light as an emergency. California's OBD II rule requires the light to blink once per second while the engine is misfiring at a level that can damage the catalytic converter ^[1]. Ford's owner guide for the 2007 F-550 explains why: excessive exhaust heat during a misfire can damage the catalytic converter, the fuel system and floor coverings, and can possibly cause a fire ^[2].

If the light is flashing or the engine shakes badly, slow down, pull over where it is safe, turn the engine off and have the car towed. The fuel that did not burn in the cylinder goes into the exhaust and burns inside the catalytic converter instead. That is what overheats it. Our guide to a flashing check engine light covers this in more detail.

A steady light is not a free pass. Some engines cut fuel to a badly misfiring cylinder and keep the light steady instead of flashing it, as the same regulation allows ^[1]. Misfires can also cause stalling and hesitation, which is a hazard in traffic ^[4]. If the light is steady and the engine feels smooth, keep driving to the short, gentle trip needed to get it checked. Do not tow a trailer, climb long grades or take long highway runs.

What causes P0300?

Ignition parts are the usual suspects: worn or fouled spark plugs, weak coils, damaged plug wires and loose connectors. Because P0300 involves several cylinders, problems that all cylinders share deserve equal attention: vacuum leaks, a weak fuel pump or clogged filter, faulty injectors, sensor faults, timing problems and low compression ^{[3] [4]}.

Cause	Why it can hit several cylinders	Clue to look for
Worn spark plugs	Plugs usually wear at the same rate	Plugs past their service interval, wide gaps, fouling
Weak ignition coil or wiring	One bad coil plus marginal others	A cylinder code next to P0300 that moves when you swap coils
Vacuum or intake leak	Extra air leans out every cylinder	Hissing sound, lean codes such as P0171 or P0174
Low fuel pressure or poor fuel	All injectors share one supply	Misfires under load or after a fill-up
Carbon on intake valves	Builds up on all cylinders over time	Misfires that build up over many miles, often on direct injection engines
Crank or cam sensor, timing	The computer reads engine speed wrong	Sensor codes, misfires that seem random
Low compression	Worn valves, rings or a head gasket	Oil or coolant on plugs, low compression readings

Two more causes are easy to miss. Haynes notes that engine software can set a false P0300, so it is worth asking a dealer whether your engine has a software update before you replace parts ^[3]. And a lean condition shows up as P0171 or P0174: if you have one of those with P0300, chase the air leak or fuel supply first. A rough engine at a stop is often the first sign; see why an engine idles rough.

How do you diagnose P0300?

Work from the cheapest and safest checks to the most involved. Do not clear the code before you write down the freeze frame data, because clearing erases the snapshot of conditions when the misfire happened. Haynes gives the same order: scan first, then inspect, then test ^[3].

1. Scan and record. Save every stored and pending code, plus the freeze frame (engine speed, load and temperature when the code set). If your scanner shows misfire counts per cylinder, note which cylinders lead. Our OBD2 scanner guide shows where to find these screens.
2. Read the pattern. Misfires only when cold, only at idle or only under hard acceleration each point to different causes. Lean codes point to air or fuel.
3. Look and listen. With the engine off and cool, check vacuum hoses for cracks, plug wires for damage and coil connectors for looseness. With the engine idling, listen for a hiss near the intake.
4. Check the plugs. Pull the spark plugs and look for wear, fouling, oil or a wrong gap ^[4]. Oil on several plugs suggests the engine is burning oil.
5. Swap a coil. If a cylinder code shows up with P0300, move that cylinder's coil to another cylinder, clear the codes and drive. If the misfire follows the coil, the coil is bad ^[3].
6. Hand off the harder tests. Fuel pressure tests, smoke tests for hidden vacuum leaks and compression tests need special tools. Direct injection engines run very high fuel pressure, so have a qualified technician check the fuel system.

How do you fix P0300, and what does it cost?

The fix is whatever the diagnosis found: new spark plugs, a coil, a vacuum hose, a fuel pump or injector, a sensor, or engine work for low compression. We do not list prices here because we could not find a current, reliable range for November 2026. What drives the cost is clear, though:

• The failed part. A cracked vacuum hose costs far less than a fuel pump or a head gasket job.
• Engine layout. On some engines the spark plugs and coils are hard to reach, which adds labor time.
• How many cylinders need parts. Plugs are usually replaced as a set.
• Whether the catalytic converter was damaged. Driving on a hard misfire can turn a small repair into a large one. If the converter does need replacing, use a legal replacement part: removing or disabling emissions equipment is illegal under the Clean Air Act, which prohibits tampering with emissions controls ^[5]. A converter damaged by heat can later set P0420.

After the repair, clear the code and drive normally. Clearing a code does not fix anything; it only resets the light. California's rule also lets the light turn off on its own after three drive cycles in similar conditions without the misfire returning ^[1]. For inspection, a car with the check engine light on will not pass a California Smog Check, and after a battery disconnect the Bureau of Automotive Repair suggests driving for a week or two so the readiness monitors can reset ^[6].

Which vehicles get P0300 most often?

Any gasoline engine can set P0300, and we found no public data that ranks makes by how often it appears. Some manufacturers have published bulletins about it, though. General Motors bulletin 16-NA-383 covers rough idle and misfire codes P0300 to P0308 on 2000 to 2025 GM gasoline engines, caused by carbon buildup on the valves or sticking valves ^[7]. Our P0300 on Chevrolet article covers that bulletin. If you are not sure what your code means, try the code lookup tool.