P0301 fault code: cylinder 1 misfire
Plain-language definition
Cylinder 1 Misfire Detected
What does it mean?
A misfire is when the fuel-air mixture in a cylinder doesn't ignite at all or burns only partly. On most cars the engine computer monitors the crankshaft's rotation speed through the crank sensor; when there's no combustion in a cylinder, the crankshaft slows down for an instant. By looking at the crankshaft position where the slowdown happens, the engine computer works out which cylinder the misfire is coming from.
P0301 means the misfires in cylinder 1 have gone past the limit set by the engine computer. The code tells you where the problem is but not what's causing it: it could be that cylinder's spark plug, coil or injector, or a mechanical problem in the cylinder itself. Which cylinder counts as number 1 can vary by engine and manufacturer.
You may notice the engine shaking, running unevenly, especially at idle or under load, and losing pulling power. As the misfires become more frequent, the check engine light may flash.
How serious is it?
It's rated Priority: even a misfire in a single cylinder can send unburned fuel into the exhaust and make the catalytic converter overheat.
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 plug (on petrol engines)
- This cylinder's ignition coil or spark plug wire
- Clogged or leaking injector on this cylinder
- Air leak in the intake passage to this cylinder (manifold gasket)
- Low compression (valves, piston rings or 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 1 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.