OBD-II Code · Powertrain
P0300
Random/Multiple Cylinder Misfire Detected
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.
Common symptoms
- Rough idle
- Check engine light flashing or solid
- Loss of power
- Engine shaking
- Poor fuel economy
Likely causes
- Worn spark plugs
- Faulty ignition coils
- Vacuum leak
- Bad fuel injectors
- Low fuel pressure
- Clogged catalytic converter
Where to start
- Try the cheapest cause first. Start by checking: worn spark plugs.
- Cost & scope. $50-$500 depending on cause. Spark plugs are cheapest; catalytic converter is most expensive.
- If the code returns after the fix: escalate to a shop or scanner with live-data and freeze-frame. A code that re-sets means the underlying fault is still there. Don't keep driving with this one active — risk of damage.
Read the full diagnostic procedure
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 patterns
Vehicle-specific patterns: 2008-2017 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 and aftermarket "iridium-tip" plugs from auto-parts stores wear early. 2007-2014 Ford 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. 2010-2015 BMW 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). 2005-2010 Chrysler Hemi 5.7L will throw P0300 with the MDS (multi-displacement) cylinders if a lifter fails — listen for ticking before assuming spark/fuel.
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