P0300 means the engine control module detected misfires on multiple cylinders, or misfires it could not attribute to a specific cylinder, at a rate above its threshold. The single-cylinder codes P0301 through P0312 name the cylinder; P0300 is stored when the count is spread across cylinders or the pattern is too irregular to assign. Most calibrations store P0300 together with the individual codes for the cylinders that contributed most.
Severity: moderate, high if the light flashes. Can you keep driving? Only if the light is steady. A flashing check engine light means the misfire rate is high enough to send unburned fuel into the catalytic converter and overheat it, and the correct response is to stop; see flashing versus steady. A steady light with a slight roughness can be driven to a shop, but not for weeks: a misfire that persists kills the converter and, on direct-injection engines, washes oil from the cylinder walls.
The family, the swap test and the location of each cylinder are covered in P0300 misfire codes and P0304; this page is the deep version for the random or multiple case.
How the computer counts a misfire
There is no combustion sensor on most engines. The module watches the crankshaft position sensor: each power stroke should accelerate the crankshaft slightly, and a cylinder that does not fire shows as a momentary slowdown at the moment it should have. The module knows which cylinder was due from the camshaft sensor, so it can count misfires per cylinder over 200 and 1,000 revolution windows. Above a first threshold it stores a pending code; above a second, the catalyst-damaging rate, it flashes the light.
Three consequences:
- Anything that makes the crank speed irregular can be counted as a misfire. A rough road with a worn flexplate, a failing dual-mass flywheel, a driveline vibration, or a crankshaft sensor reluctor with a damaged tooth produce "misfires" with perfect combustion. Most calibrations suspend counting on rough roads using the ABS wheel speed sensors, which is why a P0300 that appears only on gravel is worth a second look.
- The counting itself is a calibration. Several of the bulletins below are software, because the original counting flagged misfires that were not there, or missed the pattern of a real fault.
- "Random" is information. A fault on one injector, one coil or one plug counts on one cylinder. A fault that counts everywhere is upstream of the cylinders: fuel supply, metered air, ignition supply, valve timing, or the engine's mechanical health across the board.
What the manufacturers documented
Honda CR-V 2017 to 2018 (Service Bulletin 19-037, June 2019): P0300 through P0304 or P0172, and a whirling noise from the engine. Honda extended the powertrain warranty to six years with unlimited mileage for engine components including camshafts, rocker arm assemblies and spark plugs damaged by the underlying condition, and directs technicians to complete earlier bulletins first. On these engines a random misfire could be a valvetrain problem under warranty rather than a tune-up.
GM V6 and V8 pushrod engines 2002 to 2025 (bulletin 19-NA-219, November 2024, replacing PIP4138): misfire codes P0300 through P0308 with a chirp, squeak, squeal or tick. The diagnostic tip is that the noise identifies a valvetrain component as the source, and the bulletin steers the technician away from ignition parts toward the lifters, rockers and pushrods. Also 20-NA-098 (May 2020) for 2014 to 2020 V6 and V8 engines: guidelines for fuel injector replacement when P0300 to P0308 and the fuel trim codes set, requiring an injector fault be confirmed before a set is replaced.
Toyota Highlander Hybrid 2017 to 2019 (T-SB-0148-19, October 2019): P0301 through P0306, corrected by reprogramming the engine computer and replacing an ignition coil, under the federal emissions warranty. Software and one coil, not a set.
Ford F-150 2018 with the 2.7 L EcoBoost built on or before 12 July 2018 (TSB 18-2310, October 2018): P0300, P0316, P0301 through P0306 with the lean, rich and imbalance codes, corrected by replacing the six high-pressure direct injectors with clips, tubes and gaskets. A random misfire from injectors, on every cylinder at once.
Dodge Hornet 2023 with the 2.0 L turbo built January 28 to March 9, 2023 (TSB 18-079-23, June 2023): P0300 through P0304 with poor running, cause a spark plug cracked during installation at the factory. The oldest cause in the book, on a brand-new engine.
Ram 1500 2025 with the 3.0 L Hurricane built on or before January 15, 2025 (TSB 08-031-25, February 2025): P0300 through P0306, P0420 and P0430, and ignition coil fuse codes, corrected by updating the ignition system control module software.
Ram ProMaster City 2019 with the 2.4 L (TSB 18-068-19, October 2019): P0300 and the cylinder codes, addressed by a PCM flash.
Plugs, injectors, a coil, a valvetrain, and software on three vehicles. The count is a starting point, not a verdict.
Causes, in the order they are found
Spark plugs worn across the board, past their interval or the wrong heat range; the misfire shows under load first, when the wider gap needs more voltage than the coils can give.
A fuel supply problem: low fuel pressure from a weak pump or a clogged filter, or fuel contaminated with water or the wrong grade. All cylinders starve together under load.
A vacuum leak large enough to lean the whole engine at idle: an intake manifold gasket, a brake booster hose, a PCV hose. Usually with P0171 or P0174; see P0171 and vacuum leaks.
A shared ignition supply or ground: a coil pack feed, a ground strap, or an ignition module. Several cylinders drop out together intermittently.
Injectors failing as a set, as on Ford's 2.7 L, or carboned direct injectors on an engine with a long history of short trips.
Valve timing off: a stretched chain, a jumped tooth, a cam phaser stuck, often with P0011 through P0025 and a rough idle that is worse than the misfire count suggests; see P0011.
Low compression across cylinders: worn rings, a head gasket, valves out of adjustment on engines that need it. Confirmed by a compression or leak-down test.
A valvetrain fault making noise, as GM's tip says, or the CR-V's rocker arm condition.
A mechanical vibration counted as misfire: a flexplate or flywheel, a crankshaft sensor reluctor with a damaged tooth, a driveline problem.
A calibration, as on the Ram, the ProMaster City and the Highlander Hybrid.
The module, last.
A diagnostic order for a misfire that is everywhere
- Record every code and the misfire counters per cylinder. The counters tell you whether the misfire is truly even (a shared cause) or concentrated on two or three cylinders (look at what those share: a coil pack, a bank, an injector feed). Pull the freeze frame: engine speed, load and coolant temperature at the fault separate a cold-start misfire from one under load.
- Check for a bulletin on the exact engine. On the vehicles above the answer ranges from a plug to a flash.
- Look at the plugs. Their condition and gap, and the color of every plug, tell you about mixture, oil consumption and coolant in one look. Replace them if they are due; on many random misfires this is also the repair.
- Check fuel pressure at idle and under a snap throttle, and fuel trims: trims strongly positive at idle mean a leak, strongly positive under load mean supply, strongly negative mean rich.
- Smoke the intake for leaks if the trims point there.
- Check for noise: a tick, chirp or squeak at idle and with engine speed is the valvetrain, per GM's tip.
- Check cam and crank correlation on the scan tool; a correlation off by a few degrees is timing.
- Relative compression test with the scan tool (cranking, fuel disabled) or a gauge, if the plugs, fuel, air and timing pass.
- Look for a mechanical source of crank speed irregularity when everything else passes: flexplate cracks, the crankshaft sensor reluctor, driveline.
- Repair the cause, clear the code, and verify with the misfire counters at zero through idle, cruise and load, then let the readiness monitors complete before an inspection.
What P0300 does not tell you
It does not tell you which part failed; it tells you the failure touches more than one cylinder. Plugs, fuel, air, ignition supply, timing, compression, a valvetrain, a vibration and the software that counts all produce it. The single-cylinder codes are the module's best guess at where the count is concentrated, and the counters per cylinder are more useful than the codes; the general principle is covered in what a trouble code does not tell you.
Frequently asked questions
Can I drive with a P0300 code?
If the check engine light is steady and the engine only feels slightly rough, yes, to a shop. If the light flashes, stop; the misfire is damaging the catalytic converter and the correct response is a tow.
What is the difference between P0300 and P0301?
P0301 means the misfire was counted on cylinder 1; P0300 means it was counted on multiple cylinders or could not be assigned to one. P0301 points at a part on that cylinder (plug, coil, injector, compression). P0300 points at something shared: fuel supply, metered air, ignition supply, valve timing, plugs worn as a set, or the engine's mechanical condition.
Is P0300 always spark plugs?
No, but worn plugs are the most common single cause of a misfire across all cylinders, and on the 2023 Dodge Hornet the cause was a plug cracked at the factory. Fuel pressure, a vacuum leak, injectors failing as a set (Ford's 2018 2.7 L), valve timing and a valvetrain fault (Honda's 2017 to 2018 CR-V, GM's pushrod engines) each produce the same code, and on three vehicles the fix was software.
Why does P0300 set only on rough roads?
Because the module counts misfires from crankshaft speed, and a rough road, a worn flexplate or a driveline vibration jolt the crankshaft in a way that looks like a misfire. Most calibrations suspend counting on rough roads using the wheel speed sensors; when they do not, or when a mechanical source of vibration exists, the code sets with perfect combustion.
How much does it cost to fix P0300?
Spark plugs are inexpensive. A fuel pump or an intake gasket is a moderate repair. Injectors range from moderate to major on direct injection. Valve timing or valvetrain repairs are major. A software update is an hour at a dealer and may be covered, as on the vehicles with bulletins.
Related codes
- P0301 to P0308: cylinder-specific misfires; see P0301 and P0304.
- P0171 / P0174 / P0172 / P0175: mixture codes stored alongside when fuel or air is the cause.
- P0011 to P0025: camshaft timing codes stored alongside when timing is the cause.
- P0316: misfire detected on start-up in the first 1,000 revolutions.
- P0420 / P0430: catalyst efficiency, the consequence of a misfire driven on; see P0420.
The code number itself tells you the family and the domain; how to read an OBD2 code number explains what each character means.