CodelampCode explained
P0300: your engine is misfiring in more than one cylinder
P0300
- In plain words
- More than one cylinder, or no single one, is misfiring.
- Standard name
- Random/Multiple Cylinder Misfire Detected
- System
- Ignition and misfire
General information, not a mechanic's diagnosis: have a mechanic confirm before any repair.
What the computer saw
A misfire is a cylinder that fails to burn its fuel on a stroke. The computer spots it as a tiny stumble in how fast the crankshaft spins. P0300 means the misfires are random or spread over several cylinders. A code from P0301 to P0308 names one cylinder.
Likely causes, most common first
- Worn spark plugs. Old plugs need more voltage to fire and start to miss, often in several cylinders at once.
- Weak ignition coils or plug wires. One failing coil usually sets a single-cylinder code, but several weak ones, or a shared part, can set P0300.
- A vacuum leak or lean mixture. Too much air makes the mixture hard to light in every cylinder. A lean code (P0171, P0174) beside it points here.
- Fuel delivery. Low fuel pressure, dirty injectors or a tank of bad fuel.
- A mechanical problem. Low compression, a worn camshaft or valve trouble. Less common, and a shop finds it with a compression test.
What you can note yourself
- Note whether the check engine light is steady or flashing, and tell the shop which. It matters to how they treat the job.
- Note any cylinder code (P0301 to P0308) stored with it. It tells the shop where to look first.
- Note when it shakes: at idle, when cold, on hills, in rain or right after filling up.
- Note when the spark plugs were last changed, if you know.
What to tell the shop
- Every code, and whether the light flashed.
- When the misfire happens and how it feels.
- When the plugs and coils were last replaced.
This page gives no verdict on whether a car is safe to drive; a mechanic can.