P0301 Code: Cylinder 1 Misfire Causes and How to Fix It

P0301 means Cylinder 1 Misfire Detected: the computer has counted misfires in cylinder 1 specifically. Because the fault is in one cylinder, the cause is usually something that cylinder does not share with the others, such as its spark plug, coil, injector or valves.

What P0301 means

The engine computer detects misfires by watching small changes in crankshaft speed: each cylinder that fires speeds the crankshaft up slightly, and one that does not leaves a gap. P0300 means misfires are random or spread over several cylinders, while P0301 to P0308 name a specific cylinder. A flashing check engine light means the misfire is severe enough to overheat the catalytic converter.

Where is cylinder 1?

P0301 can appear on any engine with at least 3 cylinders; on inline engines, cylinder 1 is the first from the front (timing chain or belt end). Cylinder numbering follows the manufacturer, not a universal rule:

Driver side means the left side as you sit in the seat. For V6 engines and other layouts, check the numbering in our firing order and cylinder numbering guide.

P0301 symptoms

• Rough idle or shaking, often worse when cold
• Hesitation or loss of power under load
• Flashing check engine light during hard acceleration
• Fuel smell from the exhaust

Common causes of P0301

• Worn or fouled spark plug in cylinder 1
• Failed ignition coil or plug wire on cylinder 1
• Clogged or leaking fuel injector for cylinder 1
• Vacuum leak at the intake runner or gasket near cylinder 1
• Low compression from a burnt valve, worn rings or a head gasket leak
• A collapsed or sticking lifter or a worn camshaft lobe

On GM V8s with Active Fuel Management and Chrysler Hemis with MDS, cylinder 1 is one of the four cylinders (1, 4, 6 and 7) that shut off at light load, and the special lifters on those cylinders are a known failure point; a ticking noise with a P0301 code is a reason to read lifter tick and AFM lifter failure and the Hemi tick guide.

How to diagnose P0301

1. Swap the cylinder 1 ignition coil with a neighboring cylinder, clear the code and drive: if the misfire moves to that cylinder, the coil is bad
2. If the misfire stays, pull and inspect the spark plug for wear, oil fouling or a cracked insulator, and swap it the same way
3. Swap or test the injector, or listen to it with a mechanic’s stethoscope
4. Run a compression test on cylinder 1 and compare it with the others; follow up with a leak-down test if it is low
5. Smoke-test the intake for leaks near that cylinder

Can you drive with P0301?

Short, gentle trips are usually possible with a steady light, but a misfiring cylinder washes oil off the cylinder wall with raw fuel, and a flashing light means the catalytic converter is at risk. Fix it promptly.

Will P0301 clear itself?

If the fault stops, the computer turns off the check engine light by itself after several drive cycles without seeing it again, and the code stays in memory as history for a while. Clearing P0301 with a scan tool after a repair is fine, but if the cause is still there the code returns, sometimes within one drive. Disconnecting the battery also clears codes on most vehicles, but it erases learned fuel trims and idle settings as well.

Related codes

Guides that help

• bad ignition coil symptoms
• bad spark plug symptoms
• spark plug wires
• engine misfire and flashing check engine light
• compression and leak-down tests
• fuel injector symptoms
• lifter tick and AFM lifter failure

When it is more than a sensor

If a compression or leak-down test shows a burnt valve, broken ring or failed head gasket, the decision becomes repair versus replacement; see engine replacement cost and compare engines by code on our engines page.

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