OBD-II Code · Powertrain
P0300
Random/Multiple Cylinder Misfire Detected
Severity
high
Left alone, this one tends to take other parts with it.
Can you drive it
Depends on the light
Flashing: stop as soon as it is safe to — raw fuel is reaching the catalytic converter. Steady, and it only feels rough: a short drive to a shop is usually fine. Either way, stop if it shakes hard, loses power, overheats or makes a new noise.
Indicative cost (USD)
$50–$500
Varies by vehicle, diagnosis, parts, and local labor. This is not a repair quote.
Depending on cause. Read fuel trims before buying anything — they usually name the cause.
Your engine is misfiring on multiple cylinders at random. The ECU can't pinpoint which specific cylinder is failing, so it sets this general misfire code.
How a shop works this
A random misfire is a symptom, not a fault, and the ECU could not pin it to one cylinder. That usually means the cause is something every cylinder shares — air, fuel, or a spark reference. The scan data narrows it faster than any part swap.
Write down every code that is set, not just this one.
A lean code (P0171 or P0174), a rich code, a MAF code or a fuel-pressure code sitting next to P0300 usually names the cause outright. Codes that arrive together are worth more than any of them alone.
Read the freeze-frame data, and the per-cylinder misfire counters if the scanner shows them.
Counters spread fairly evenly across the cylinders point at something shared. Counters piled onto one or two cylinders mean this is really a cylinder-specific problem wearing a P0300 label, and it should be worked as one.
Read short-term and long-term fuel trim, warm, at idle, on every bank the engine has.
Positive means the ECU is adding fuel, negative means it is taking fuel away. Read short-term and long-term together rather than either on its own. As a rule of thumb rather than a specification, correction beyond roughly plus or minus 10% is worth chasing. An inline engine has one bank; a V engine has two, and comparing them is most of the diagnostic — bank 1 near zero with bank 2 well positive means the fault is mechanical and local to bank 2, not a global fuelling problem.
Compare those trims at idle against roughly 2,000 to 2,500 rpm.
This is the comparison that separates a leak from a fuelling problem.
- Strongly positive at idle, much closer to zero at 2,000 to 2,500 rpmUnmetered air — a vacuum or intake leak. At idle the leak is a large share of everything the engine is breathing; at higher rpm it is swamped by it, which is why the number improves. Go find the leak.
- Positive at idle and still positive as the rpm comes upFuelling or measurement, not a leak. Fuel pressure at the rail, a MAF reading low for the engine, or an exhaust leak ahead of the upstream oxygen or air-fuel sensor letting fresh air past it.
- NegativeThe ECU is pulling fuel out, so the engine is running rich rather than lean. Look at a leaking injector, a purge valve stuck open, or fuel pressure that is too high.
Sanity-check the MAF reading against the size of the engine.
A rough sanity check at warm idle is around 1 gram per second per litre of displacement — near 2 on a 2.0-litre four, near 5 on a 5.0-litre V8. Displacement and conditions move it a lot, so treat it as a smell test rather than a spec. A MAF reporting low makes the ECU under-inject, which reads as lean everywhere at once.
Only now go to parts, and take the likely-causes list in the order it is given.
Look for an obvious vacuum leak first. If you cannot find one and the trims have not told you where to go, this is the point where a shop with a smoke machine and a scanner costs less than buying parts to find out.
A flashing check-engine light means the misfire is putting raw fuel into the catalytic converter, which can destroy it quickly. Stop driving as soon as it is safe to. A steady light with a mild misfire is less urgent, but stop anyway if it shakes hard, loses power, overheats, or makes a noise it was not making before.
If the code comes back after a repair, the underlying fault is still there. That is the point to bring in a scanner with live data and freeze-frame, or a shop that has one.
Common symptoms
- Rough idle
- Check engine light flashing or solid
- Loss of power
- Engine shaking
- Poor fuel economy
Likely causes
- Vacuum or intake leakMost common
- Low fuel pressure
- Fuel injectors dirty or failing
- Ignition coils or coil pack
- Worn spark plugs
- Failing catalytic converter
Read the full diagnostic procedureP0300 means the engine is misfiring but the ECU can't isolate which cylinder.
P0300 means the engine is misfiring but the ECU can't isolate which cylinder. That's a different diagnostic from a P0301-P0308 (cylinder-specific) — and it almost always means the cause is something all cylinders share rather than a single component.
Top suspects in shop order
- degraded fuel (water/ethanol contamination in the tank), a vacuum leak large enough to lean out the whole intake, low fuel pressure starving every injector, or a failing ignition module/coil pack on a wasted-spark setup.
- The diagnostic step that catches 70%+ of P0300 causes in 10 minutes: scan fuel trim live data.
- Long-term + short-term fuel trims pinned above +15% on both banks means vacuum leak or low fuel pressure (lean condition); pinned below -10% means rich condition (failing fuel pressure regulator, leaking injector, or stuck-open EVAP purge).
- A flashing CEL during P0300 means cat-damaging misfire — pull over.
Vehicle-specific patterns2008-2017 Honda Accord/Civic/CR-V with the K24/R18 4-cylinder often throws P0300 when the spark plugs hit ~60k miles — Honda specs OEM iridium plugs…
- 2008-2017Honda Accord/Civic/CR-V with the K24/R18 4-cylinder often throws P0300 when the spark plugs hit ~60k miles — Honda specs OEM iridium plugs and aftermarket "iridium-tip" plugs from auto-parts stores wear early.
- 2007-2014Ford F-150 with the 5.4L 3-valve Triton frequently throws P0300 from carbon buildup on intake valves (cold-start misfires that clear after warm-up) — direct-injection makes the problem worse on later 3.5L EcoBoost versions.
- 2010-2015BMW N20 / N55 turbo I6 throws P0300 + cylinder-specific codes together when the OEM ignition coils degrade simultaneously around 80k miles (replace all six as a set, not one).
- 2005-2010Chrysler Hemi 5.7L will throw P0300 with the MDS (multi-displacement) cylinders if a lifter fails — listen for ticking before assuming spark/fuel.
Look up another code
P0300 — frequently asked
What does a P0300 code mean?
Your engine is misfiring on multiple cylinders at random. The ECU can't pinpoint which specific cylinder is failing, so it sets this general misfire code.
What causes a P0300 code?
Common causes: Vacuum or intake leak; Low fuel pressure; Fuel injectors dirty or failing; Ignition coils or coil pack; Worn spark plugs; Failing catalytic converter.
What are the symptoms of a P0300 code?
Typical symptoms: Rough idle; Check engine light flashing or solid; Loss of power; Engine shaking; Poor fuel economy.
Is it safe to drive with a P0300 code?
Depends on the light. Flashing: stop as soon as it is safe to — raw fuel is reaching the catalytic converter. Steady, and it only feels rough: a short drive to a shop is usually fine. Either way, stop if it shakes hard, loses power, overheats or makes a new noise. Estimated repair: $50-$500 depending on cause. Read fuel trims before buying anything — they usually name the cause..
How do I diagnose a P0300 code?
A random misfire is a symptom, not a fault, and the ECU could not pin it to one cylinder. That usually means the cause is something every cylinder shares — air, fuel, or a spark reference. The scan data narrows it faster than any part swap. 1. Write down every code that is set, not just this one. 2. Read the freeze-frame data, and the per-cylinder misfire counters if the scanner shows them. 3. Read short-term and long-term fuel trim, warm, at idle, on every bank the engine has. 4. Compare those trims at idle against roughly 2,000 to 2,500 rpm. 5. Sanity-check the MAF reading against the size of the engine. 6. Only now go to parts, and take the likely-causes list in the order it is given.
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