P0301 Code: Cylinder 1 Misfire Detected

🟠 Moderate severity · drivable

Short drives with a steady light are usually OK, but a misfire sends unburned fuel into the catalytic converter — fix it soon, and stop immediately if the light flashes.

What P0301 means

The engine computer has detected that cylinder 1 isn't firing properly and is failing to contribute its share of power. Unlike P0300 (a random misfire that jumps between cylinders), P0301 is a single-cylinder code — which actually narrows the diagnosis: the fault is almost always something specific to cylinder 1, such as its spark plug, ignition coil, or fuel injector, rather than a shared fuel or air problem.

Symptoms

Check engine light on (flashing if the misfire is severe)
Rough idle or a shaking engine
Loss of power and hesitation under acceleration
Poor fuel economy

Common causes

most common: Worn or fouled spark plug on cylinder 1
common: Failing ignition coil or plug wire for cylinder 1
common: Clogged or leaking fuel injector on cylinder 1
less common: Low compression in cylinder 1 (worn rings, a burnt valve, or a gasket leak)

How to fix it

Fix	DIY?	Typical cost
Swap the cylinder 1 spark plug and coil with another cylinder to see if the misfire follows the parts	Yes	$0–20
Replace the cylinder 1 spark plug	Yes	$10–50
Replace the cylinder 1 ignition coil	Yes	$50–200
Have a compression test performed on cylinder 1	Mechanic	$100–200

Frequently asked questions

Does P0301 mean the problem is only on cylinder 1?

Usually yes. A single-cylinder misfire points to that cylinder's own spark plug, coil, or injector. If the misfire moves between cylinders, you're more likely to see P0300 instead.

What should I check first on a P0301?

Do a free swap test: move cylinder 1's spark plug and coil to another cylinder. If the misfire moves to the new cylinder, you've found the bad part. If it stays on cylinder 1, suspect the injector or low compression.

Where is cylinder 1 located?

Cylinder numbering varies by engine, so check your vehicle's firing-order diagram. On most inline engines, cylinder 1 is the one nearest the front of the engine (the accessory-drive/timing end).