P0301 Cylinder 1 Misfire Detected

P0301 indicates a detected misfire on cylinder 1. The code identifies the cylinder, but the cause can still be ignition, fuel, compression, air, or control related.

Code details

Generic OBD-II · P0

System: Ignition / Misfire
Code type: Generic (SAE / ISO controlled)
Standard: SAE J2012 / ISO 15031-6

Diagnostic boundary

A diagnostic trouble code reports that a monitored test failed. It does not prove one specific part is bad, and manufacturer logic can add vehicle-specific conditions.

Do not assume the coil is bad just because cylinder 1 is named; prove whether the fault follows spark, fuel, compression, or wiring.

Symptoms of P0301

Rough idle or a distinct shake, often worse at low RPM.
A stumble or dead spot traced to cylinder 1.
A flashing check-engine light when the misfire is active.
Slight power loss and worse fuel economy.

Common causes of P0301

A worn spark plug or failed ignition coil on cylinder 1.
A clogged, leaking, or dead injector on cylinder 1.
A vacuum leak or low compression local to that cylinder.
Carbon-tracked plug boot or damaged coil wiring.

Useful checks before replacing parts

Compare cylinder 1 misfire counts with neighboring cylinders under idle, cruise, and load.
Swap-test ignition parts only when safe and appropriate, then confirm whether the misfire follows the part.
Check injector operation, compression, leakdown, vacuum leaks near that runner, and connector condition.

Related OBD-II codes

These nearby ignition / misfire entries can help compare wording and pin down the fault area.