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.

P0301moderate severityGenerally driveable

P0301 Code: Cylinder 1 Misfire Detected

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 likely

Fix: 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.

DIY ~$10Shop ~$80

spark plugs repair guide

#2 Failed ignition coil for cylinder 1

likely

Fix: 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.

DIY ~$35Shop ~$130

ignition coil repair guide

#3 Faulty fuel injector on cylinder 1

possible

Fix: 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.

DIY ~$50Shop ~$300

fuel injector repair guide

#4 Low compression in cylinder 1 (worn rings, damaged valve, or head gasket leak)

possible

Fix: 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.

DIY ~$20Shop ~$1800

Get a FREE OBD2 scan first — no purchase required

AutoZone, O'Reilly Auto Parts, and Advance Auto Parts all scan your car's computer for free. Walk in, they plug in a scanner, you get a code in under 2 minutes. Then come back here and look up that code at eli5cars.com/obd2 for the plain-English explanation.

Pro tip: Take a photo of the code before they clear it.

P0301 Code: Cylinder 1 Misfire Detected

Most likely causes — ranked

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Frequently asked questions