What P0301 Means
The engine control module has detected a misfire specifically in cylinder 1 — this cylinder isn't burning fuel properly on every cycle.
Common Causes
- Worn or fouled spark plug in that cylinder
- Failing ignition coil for that cylinder
- Faulty or clogged fuel injector for that cylinder
- Low compression in that cylinder (worn rings, valve, or head gasket)
- Damaged or disconnected spark plug wire (on older coil types)
Symptoms You Might Notice
- Rough idle, often with a noticeable single-cylinder shake
- Engine hesitation or stumble under load
- Check engine light, flashing if the misfire is severe
- Popping or ticking sound from the exhaust
What to Check First
- 1
Swap the spark plug and ignition coil from cylinder 1 with another cylinder to see if the misfire follows the part
- 2
Inspect the fuel injector for that cylinder for clogging or electrical faults
- 3
Run a compression test on that cylinder specifically to rule out a mechanical issue
- 4
Check for oil in the spark plug well, which can indicate a valve cover gasket leak causing plug fouling
Frequently Asked Questions
Do I need to replace all spark plugs or just cylinder 1's?
Start with just the affected cylinder's plug and coil. If the misfire clears, you likely found the cause. If plugs are old and due for replacement anyway, doing all of them at once is common practice.