P0304 fault code: cylinder 4 misfire
Plain-language definition
Cylinder 4 Misfire Detected
What does it mean?
On most cars the engine computer monitors combustion in each cylinder through small fluctuations in the crankshaft's rotation speed. When the mixture in cylinder 4 doesn't ignite or burns only partly, the crankshaft turns more slowly than expected at that moment; once these events go past a set rate, P0304 is stored.
The code only tells you there's a misfire in this cylinder; it doesn't show the cause. If P0300 or misfire codes for other cylinders are stored along with P0304, the problem may come from a common source affecting more than one cylinder. If the code is on its own, the cause is usually in a part that belongs to this cylinder.
You may notice the engine shaking, the idle speed going up and down, or pulling power dropping as you accelerate. There may be a smell of unburned fuel from the exhaust; when the misfiring intensifies, the check engine light may flash.
How serious is it?
A misfire in a single cylinder is also rated Priority. The main reason is that unburned fuel can pass into the exhaust and overheat the catalytic converter.
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 spark plug (on petrol engines)
- This cylinder's ignition coil or spark plug wire
- Clogged or leaking injector
- Loose or corroded connector
- Air leak at the intake manifold gasket
- Low compression (valves, piston rings, cylinder head gasket)
The list shows general causes; a workshop finds the actual cause on your car with a check.
Related codes
How does it appear in the 2dakika report?
Cylinder 4 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.