P0301

P0301: Cylinder 1 Misfire Detected — Causes, Fixes & Cost

P0301 means your engine's cylinder 1 isn't firing correctly. The ECU detected that combustion in cylinder 1 is incomplete or not happening at all. It's one of the most common misfire codes and is often a straightforward fix — but ignoring it will trash your catalytic converter.

🔧 Common Causes

Faulty spark plug in cylinder 1 (most common)
Bad ignition coil for cylinder 1
Leaking or clogged fuel injector on cylinder 1
Low compression (worn rings, burned valve)
Vacuum leak near cylinder 1 intake
Faulty fuel injector driver circuit

⚠️ Symptoms You'll Notice

Check Engine Light on, sometimes flashing
Rough idle (noticeably uneven)
Engine shakes at idle or under acceleration
Reduced power and sluggish throttle response
Poor fuel economy
Exhaust smells rich (unburned fuel)

Estimated Repair Cost

DIY Cost

$15–$60 (spark plug + coil for cylinder 1)

Parts only

Shop Cost

$120–$400 depending on cause

Parts + labor

DIY Fix Path — Cheapest First

Work through these in order. Most people fix it by step 2.

1

Replace Spark Plug in Cylinder 1

$5–$15

The cheapest and most common fix. Remove the plug from cylinder 1 and inspect — if it's fouled, cracked, or worn, replace it. Total job: 15 minutes.
2

Swap Coil Pack to Test

$30–$60

Move the ignition coil from cylinder 1 to another cylinder and clear the codes. If the misfire moves with the coil (now P0302, P0303, etc.), the coil is bad. Replace it.
3

Clean or Replace Fuel Injector on Cylinder 1

$15–$50

Add injector cleaner to the tank ($15) as a first step. If the code persists, a clogged or leaking injector on cylinder 1 may need replacement or professional cleaning.
4

Compression Test

$0 (DIY tool rental) – $80 at a shop

If plugs and coil both check out, do a compression test on cylinder 1. Low compression points to worn rings or a burned valve — a more serious (and expensive) repair.

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Frequently Asked Questions

How do I know which cylinder is cylinder 1?

Cylinder numbering varies by engine. On most inline-4 engines, cylinder 1 is closest to the timing belt/chain (front of the engine). On V6/V8 engines, consult your service manual — it"s usually the front-left. Your VIN decode or a Nova's Iron Pulse diagnosis will confirm the layout for your specific vehicle.

P0301 keeps coming back after I replace the spark plug — why?

If the code returns after a plug replacement, the ignition coil for cylinder 1 is likely bad. Swap the coil from cylinder 1 to another cylinder and clear codes — if the misfire follows the coil (now showing P0302, P0303, etc.), replace the coil.

Can a bad fuel injector cause P0301?

Yes. A stuck-open injector floods the cylinder with fuel (rich misfire), while a clogged injector starves it (lean misfire). Both trigger P0301. You can test injectors with a stethoscope (clicking sound) or an injector tester.

How urgent is P0301?

Urgent if the light is flashing. A steady CEL gives you more time, but every mile driven with a misfire risks $1,000+ in catalytic converter damage. Fix it within a week.