P0301: Cylinder 1 Misfire Detected
P0301 means the engine computer has detected that cylinder 1 is misfiring, so it is not burning its fuel properly. A steady check engine light means you should get it fixed soon, and a flashing light means you should stop driving as soon as it is safe because the catalytic converter can be damaged.
You can drive, but get it checked soon
With a steady light and mild symptoms, a short drive to a repair shop is generally acceptable. If the light flashes, the misfire is at a rate that can damage the catalytic converter, so reduce load and stop driving as soon as it is safe.
What it means
The engine computer watches crankshaft speed (how smoothly the engine's main rotating shaft spins). A cylinder that does not fire gives no push, and the computer notices the missing impulse. P0301 is set when more than 90 % of the detected misfires come from cylinder 1. If the misfire rate is high enough to damage the catalytic converter (the emissions part in the exhaust), the check engine light flashes. At a lower, emissions-relevant rate the light comes on after two trips. Some Ford and GM engines may shut off the injector of a misfiring cylinder to protect the catalyst, and the engine can go into limp mode (reduced power).
Likely causes
- Faulty ignition coil on cylinder 1 (coil, connector or ground)Very likely
The coil creates the spark for that cylinder, and if it or its wiring fails, the cylinder does not fire.
- Worn, sooted, cracked or wrongly gapped spark plug on cylinder 1Very likely
A plug in poor condition cannot light the fuel mixture reliably.
- Clogged or leaking injector on cylinder 1, or a fault in its controlPossible
If the injector delivers too little or too much fuel, or is not triggered, the cylinder misfires.
- Low compression on cylinder 1 (valve, piston rings, head gasket) or a local air leakLess likely
Without enough compression, the mixture will not ignite properly even with good spark and fuel.
- Water or oil in the spark plug wellLess likely
Liquid in the well can weaken or short out the spark.
What you may notice
- Check engine light on, flashing when the misfire could damage the catalytic converter
- Rough idle, jerking or vibration
- Loss of power or hesitation when accelerating
- Smell of unburnt fuel and higher fuel consumption
What to check, cheapest first
- 1Read the code and any stored freeze-frame data with an OBD-II scanner, and check whether other misfire codes such as P0300 are also stored. · you can do it
- 2Look at the cylinder 1 coil connector and wiring for damage, looseness or corrosion, and check the plug well for water or oil. · you can do it
- 3Swap the cylinder 1 ignition coil with a neighboring cylinder's coil, clear the code, and see whether the misfire moves to that cylinder. · you can do it
- 4Remove the cylinder 1 spark plug and inspect it for wear, soot, cracks and correct gap; if the misfire stays with the cylinder, swap plugs the same way as the coil. · you can do it
- 5Test the cylinder 1 injector and its control signal, and check for a local air leak. · mechanic
- 6Run a compression test on cylinder 1 if coil, plug and injector are fine. · mechanic
Related codes
Frequently asked questions
Can I drive with a P0301 code?+
A short trip with a steady light is generally acceptable, but don't drive far. If the light flashes, stop as soon as it is safe, because the misfire can damage the catalytic converter.
Can a bad spark plug cause P0301?+
Yes. A worn, sooted, cracked or wrongly gapped plug on cylinder 1 is one of the two most likely causes, along with the ignition coil.
Will P0301 pass an emissions test?+
Not with the light on. The code is emissions-relevant, so the fault must be repaired and the system needs to complete its drive cycle (a set pattern of driving that lets the computer re-run its self-tests) before it will be ready for a test.
How hard is it to fix P0301?+
The repair is rated easy and can often be done at home. Time ranges from about 0.3 to 4 hours depending on the cause.
Written with the help of AI from the public OBDex definition (CC0). Each make may use the code differently. Updated: 2026-11-10