P0301: Cylinder 1 Misfire Detected
The computer detected that cylinder 1 is not firing correctly often enough to raise emissions or hurt the engine.
What P0301 means
P0301 is a cylinder specific misfire code. The computer counts tiny drops in crankshaft speed and matches them to the firing order, so it knows the weak power stroke belongs to cylinder 1. Because the problem is limited to one cylinder, the cause is usually a part that serves only that cylinder: its spark plug, its coil or plug wire, its fuel injector, or its valves. That makes P0301 easier to pin down than a random misfire. Mechanics start with the swap test, moving the coil and then the plug to another cylinder and seeing if the misfire follows. If it stays put, they check the injector with a noid light or balance test and then run a compression test. Cylinder 1 sits at the front of most engines and is often easy to reach. A steady light gives you some time, but a flashing light means unburned fuel is heading into the catalytic converter and you should stop driving.
Common symptoms
- Check engine light on, or flashing when the misfire is bad
- Rough or shaky idle
- Hesitation or jerking when you accelerate
- Loss of power, especially going uphill or merging
- Worse gas mileage
Most common causes
- Worn or fouled spark plug in cylinder 1
- Failing ignition coil on cylinder 1
- Clogged or leaking fuel injector for cylinder 1
- Vacuum leak near the cylinder 1 intake runner
- Damaged plug wire or coil boot
- Low compression in cylinder 1 from a valve or ring problem
What to check yourself first
Find cylinder 1 in your repair manual; it is usually at the front of the engine, closest to the timing belt or chain. On coil-on-plug engines, swap the cylinder 1 coil with a neighbor, clear the code and drive. If the code follows the coil (for example it becomes P0302), you found the problem.
Typical fixes and what they cost
| Fix | Typical cost | Note |
|---|---|---|
| Replace ignition coil | $238-$320 | If the misfire moves to another cylinder after swapping coils, the coil is confirmed bad. |
| Replace spark plugs | $288-$399 | Shops usually replace the whole set, not just one plug, so the cylinders stay matched. |
| Replace fuel injector | $768-$953 | Needed if the injector tests clogged or electrically open. |
| Check engine light diagnosis at a shop | $125-$183 | Includes a compression or leak down test if ignition and fuel check out. |
Typical US price ranges for parts and labor, not quotes. Your shop should confirm the cause with a diagnostic before replacing parts.
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Related codes
- P0300 Random/Multiple Cylinder Misfire Detected
- P0302 Cylinder 2 Misfire Detected
- P0201 Injector Circuit/Open - Cylinder 1
- P0351 Ignition Coil "A" Primary/Secondary Circuit
- P0420 Catalyst System Efficiency Below Threshold (Bank 1)