Engine
What are engine misfires (P0300)?
A misfire is combustion that does not happen, or is incomplete, in a cylinder. The control unit detects it from small variations in crankshaft speed and stores P0300 if several cylinders are involved or P0301, P0302… for a specific one. If the light flashes, the misfires are severe and can damage the catalytic converter: slow down and go to a workshop.
Reviewed by Daniel Morales, founder of Reprorace SL, on
What causes them?
On gasoline engines the most common causes are worn spark plugs and failed ignition coils. Also injectors, vacuum leaks, low fuel pressure or poor-quality fuel.
If the problem is mechanical (low compression from valves or a head gasket), the misfire does not go away when ignition parts are replaced. On diesels it is usually the injectors or compression.
How do you find the misfiring cylinder?
The number in the code tells you (P0302, cylinder 2). With P0300, the per-cylinder misfire counters in live data or in the manufacturer's diagnostics help locate it.
Workshops often swap coils or plugs between cylinders and see whether the misfire moves with them.
Can I keep driving?
With a steady light and a slight stumble, drive gently to a workshop. With a flashing light, do not floor it and stop as soon as possible: unburned fuel overheats the catalytic converter.
General guidance only: every manufacturer and model has its own details. Always follow your vehicle's manual and, if in doubt, ask a workshop.
Related
Related trouble codes
- P0300Random or multiple cylinder misfire detected
- P0301Cylinder 1: misfire detected
- P0302Cylinder 2: misfire detected
- P0303Cylinder 3: misfire detected
- P0304Cylinder 4: misfire detected
- P0351Ignition coil A, primary control circuit open
Related symptoms
- Flashing engine warning light: what it means and what to do
- Car jerks when accelerating: causes and what to do
- Rough idle: why the engine shakes or hunts when stationary
Learn more
See what your car is saying
With the ECO-LITE you see the code and its freeze frame right away; your workshop can look live, if the car publishes them, at the per-cylinder misfire counters.
Presale price: €129 · US$129
Frequently asked questions
Can a misfire fix itself?
If it was bad fuel, it can go away once the fuel is replaced. If it is a plug or a coil, no.
Why does it only misfire when cold?
Some coils, injectors or mixture problems only show with a cold engine. The freeze frame tells you.
What does P0300 mean?
Random or multiple-cylinder misfires.