P0301 – Cylinder 1 Misfire Detected
What does P0301 mean?
The engine computer has detected a misfire specifically in cylinder 1. Unlike P0300 (random misfire), this points to a problem isolated to one cylinder, which makes diagnosis much more direct — the fault is almost always the plug, coil, injector, or compression in that single cylinder.
What causes P0301?
Listed from most to least common:
- 1Worn or fouled spark plug in cylinder 1
- 2Failing ignition coil on cylinder 1
- 3Clogged or failed fuel injector on cylinder 1
- 4Bad spark plug wire (on vehicles that use them)
- 5Vacuum leak local to cylinder 1's intake runner
- 6Low compression in cylinder 1 from a burnt valve, worn rings, or head gasket failure
Code breakdown
Common symptoms
- Check engine light on or flashing
- Rough idle with a distinct stumble
- Noticeable vibration, especially at idle
- Power loss and hesitation on acceleration
- Higher fuel consumption
How to diagnose
- 1Locate cylinder 1 for your specific engine — the position varies by manufacturer.
- 2Remove and inspect the cylinder 1 spark plug. Compare it against plugs from other cylinders.
- 3Swap the cylinder 1 ignition coil with a neighboring cylinder, clear codes, and drive. If the misfire moves to that cylinder (e.g. becomes P0302), the coil is faulty.
- 4Swap the injector the same way to test it.
- 5Perform a compression test on cylinder 1. Low compression indicates a mechanical problem rather than ignition or fuel.
- 6If compression is low, follow with a leak-down test to identify whether it is rings, valves, or the head gasket.
Unburned fuel from a misfiring cylinder can overheat and destroy the catalytic converter. A flashing check engine light means stop driving.
Common fixes and estimated costs
| Repair | Estimated cost |
|---|---|
| Replace spark plug (all cylinders recommended) | $100–$350 |
| Replace ignition coil | $100–$350 |
| Replace fuel injector | $150–$500 |
| Head gasket or valve repair | $1,200–$3,000 |
Costs are rough US estimates including parts and labor. Actual pricing varies significantly by vehicle, region, and shop rates.
Good to know
The coil-swap test is the fastest way to confirm a bad coil and costs nothing. If the misfire code follows the swapped coil to its new cylinder, you have found the fault.
Related codes
This information is provided for general reference only and may vary by manufacturer, model, and year. It is not a substitute for professional diagnosis or repair.