P0301moderate severityGenerally driveableP0301 Code: Cylinder 1 Misfire Detected
Written in plain English and reviewed by the eli5cars editorial team · Last reviewed June 2026
What it means in plain English
Your engine is like a team of runners in a relay race — each cylinder fires in sequence to keep things smooth. P0301 means runner #1 keeps dropping the baton. Cylinder 1 isn't burning fuel properly on some strokes, causing the engine to stumble and shake. The good news: the computer has given you the exact location, which makes diagnosis much faster than the scatter-shot P0300.
Most likely causes — ranked
#1 Worn, fouled, or incorrectly gapped spark plug in cylinder 1
most likelyFix: Remove the cylinder 1 spark plug (cylinders are numbered from the front/accessory side of the engine on most vehicles — check your owner's manual or a YouTube diagram for your specific car). Inspect for fouling, cracking, or excessive wear. Replace with an OEM-spec plug gapped to factory spec.
#2 Failed ignition coil for cylinder 1
likelyFix: Swap the cylinder 1 coil with an adjacent cylinder coil (e.g., swap cyl 1 and cyl 3). Clear the code and drive. If the misfire moves to the new cylinder, the coil is bad. Replace the failing coil.
#3 Faulty fuel injector on cylinder 1
possibleFix: Listen for the injector's click with a mechanic's stethoscope or a long screwdriver pressed to your ear. A dead injector is silent. Injectors can also be tested for resistance with a multimeter. Replace or clean the faulty injector.
#4 Low compression in cylinder 1 (worn rings, damaged valve, or head gasket leak)
possibleFix: Perform a compression test on all cylinders. Cylinder 1 should read within 15 psi of the others; a significantly low reading (under 100 psi on most engines) suggests internal engine wear. A wet compression test (add a teaspoon of oil to the cylinder) distinguishes ring wear from valve problems. This repair typically requires professional work.
Check engine light on? Get a free code scan
If your check engine light is on, most auto-parts stores (AutoZone, O'Reilly, Advance) will read the code for FREE — no purchase required, just walk in. Bring the code back here and look it up at eli5cars.com/obd2 for the plain-English explanation.
Note: a scan only helps when there's an active fault code. For purely mechanical symptoms (noises, vibrations, leaks), a scan may show nothing — the suspects listed above are your starting point.
Want to read the codes yourself?
First, the free option: AutoZone, O’Reilly, and Advance Auto Parts read your codes for free — no purchase needed. That’s the cheapest way to get the code to look up here. If you’d rather have your own so you can check anytime (and clear a code after a fix), the Veepeak OBDCheck BLE is an inexpensive, reliable plug-in reader that pairs with a free phone app and works on any car sold since 1996.
See the Veepeak OBD2 scanner on AmazonAffiliate link — we may earn a commission at no extra cost to you. Details.
Heads up: some links below are affiliate links (including Amazon Associates) — if you buy through them we may earn a small commission at no extra cost to you. Details: /disclosure.
Frequently asked questions
Is P0301 serious?
It's worth addressing promptly. A solid check engine light with P0301 and mild rough running is not an emergency — get it checked within a week. A flashing check engine light means the misfire is severe enough to damage the catalytic converter. Pull over and don't drive it.
How do I know which cylinder is cylinder 1?
On most inline 4-cylinder engines, cylinder 1 is at the front of the engine (closest to the drive belt/timing cover). On a V6 or V8, Bank 1 is the side of the engine containing cylinder 1 — typically the front bank on a transverse-mounted engine. Your owner's manual has a diagram, or search 'cylinder 1 location [your car make model year]' on YouTube.
I replaced the spark plug in cylinder 1 and P0301 came back. What next?
Swap the ignition coil from cylinder 1 with the coil from another cylinder. Clear the code and drive a normal cycle. If the misfire follows the coil to the new cylinder, replace the coil. If it stays on cylinder 1, the problem is the injector, compression, or something mechanical.
What does P0301 cost to fix at a shop?
If it's just a spark plug: $80–$120 including labor. If it's an ignition coil: $130–$200. If it's a fuel injector: $250–$400. If it's compression-related (rings, valves, head gasket): $1,500–$3,500 depending on the specific issue.