P0300 fault code: random misfire in multiple cylinders
Plain-language definition
Random/Multiple Cylinder Misfire Detected
What does it mean?
For the engine to run smoothly, the fuel-air mixture in each cylinder has to ignite at the right moment and burn completely. When the mixture doesn't burn at all, or burns only partly, that's called a misfire. On most cars the engine computer monitors misfires through the crankshaft position sensor (crank sensor): when there's no combustion in a cylinder, the crankshaft slows down for an instant, and the engine computer counts these small drops in speed.
P0300 is stored when the misfires aren't concentrated in a single cylinder, or when they show up in more than one cylinder. This often points to a common cause affecting more than one cylinder rather than to a single part. Cylinder-specific misfire codes such as P0301 or P0302 may be stored at the same time.
You may notice the engine shaking, idling roughly, hesitating as you accelerate or losing pulling power. Fuel consumption may go up, and there may be a smell of unburned fuel from the exhaust. If the misfiring reaches a level that can damage the catalytic converter, the check engine light may flash.
How serious is it?
It's rated Priority because fuel that doesn't burn during a misfire passes into the exhaust and can overheat the catalytic converter, damaging it permanently. Even if the symptoms are mild, it's important to find the cause.
Severity is a guide; if the warning light is flashing or you notice symptoms while driving, have the car checked at a workshop.
Common general causes
- Worn or faulty spark plugs (on petrol engines)
- Ignition coil or spark plug wire problems
- Air leak on the intake side (vacuum leak)
- Low fuel pressure (fuel pump, fuel filter)
- Dirty or faulty injectors
- Mechanical problems such as low compression (valves, piston rings, gaskets)
The list shows general causes; a workshop finds the actual cause on your car with a check.
Definitions by make
Some manufacturers record the same code under their own wording:
- Ford
- Random Misfire Detected
- Volkswagen
- Engine Misfire Detected
Related codes
How does it appear in the 2dakika report?
Random/Multiple Cylinder Misfire Detected
If the code is read as a confirmed (stored) fault, the report shows it with the "Priority" severity; in pending or past records, codes that don't request the warning light and aren't critical appear as "Info". If the engine computer stored them, the conditions when the fault was recorded (engine temperature, rpm, speed) are shown too.
Read this code with the OBD-X1, and clear it from the app after the repair.
Clearing the code doesn't fix the fault; if the problem persists, the code comes back.