P0300Random/Multiple Cylinder Misfire Detected
Caution
What it means
The engine computer times every power pulse from the crankshaft. When cylinders randomly fail to fire — the crank momentarily slows where it should surge — it logs a misfire, and P0300 means the misses are spread across more than one cylinder rather than isolated to one. You'll often feel it as a shake at idle, a stumble, or lost power.
Is it safe to drive?
Caution
It depends on the light. A steady check-engine light with a light stumble means drive gently and get it diagnosed within days, not weeks. A flashing check-engine light means unburned fuel is pouring into the catalytic converter and overheating it — ease off the throttle, avoid load, and stop driving as soon as it's safe to. A misfire ignored long enough usually turns into a P0420 and a converter bill.
Common causes
Most likely first.
- Worn spark plugs — the most common cause, especially past their service interval
- A weak or failing ignition coil (or old plug wires, where fitted)
- A vacuum leak leaning out the mixture
- Low fuel pressure — a tired pump, clogged filter, or failing regulator
- Dirty or leaking fuel injectors
- Low compression from valve or head-gasket trouble — less common, but the reason to test if the easy things check out
What the live data shows
Misfire counts per cylinder show which cylinders are missing and how badly — random scatter points at something shared (fuel supply, a vacuum leak, plugs due as a set), while one dominant cylinder points at that cylinder's plug, coil, or injector. Watch RPM at idle for rhythmic dips, and the short-term fuel trims jumping as the O2 sensors see unburned oxygen. The freeze-frame stored with the code records the RPM and load where it happened.
A scanner that reads all 139 standard sensors shows you these readings live. ScanMyCar charts them as you drive, keeps the freeze-frame stored with the code, and pulls codes from every module — free, with any cheap Bluetooth adapter.
Typical fixes
Cheapest first, where honesty allows.
- Spark plugs, if they're anywhere near due — cheap and the most likely fix
- Smoke-test or spray-test the intake for vacuum leaks
- Swap coils between cylinders and see whether the misfire follows
- Test fuel pressure; replace the filter or pump if it's low
- Compression-test if the misfire survives all of the above
A guide, not a diagnosis. This page describes what P0300 generally means across OBD-II cars. What's actually wrong with your car depends on its live data and its history — and any repair decision deserves a proper diagnosis, whether that's you with a scanner or a professional with a lift.