P0301: Cylinder 1 misfire

What P0301 means

Verified description: Cylinder 1 Misfire Detected

General OBD-II powertrain explanation for vehicles that support this code. The practical context here focuses on gasoline engines. Library coverage does not establish UTH Scanner compatibility with a vehicle or module.

Vehicle-specific limits

• Cylinder numbering depends on the engine. Find cylinder 1 in the correct service diagram instead of assuming it is the first one you can see.
• A gasoline ignition check does not translate into a diesel repair procedure. Stored and pending code status also matter when deciding whether the fault is occurring now.

What the code does and does not tell you

What it establishes

• The controller recorded a misfire associated with cylinder 1.

What it does not establish

• That the cylinder 1 ignition coil is defective.
• That every cylinder is affected, or that a code erase confirms a repair.

Symptoms you may notice

• Rough idle or uneven running may accompany the warning. The problem can be intermittent.
• The check-engine light may flash during an active severe misfire.

Possible causes

• Fuel delivery, ignition or a mechanical sealing problem can produce a cylinder-specific misfire.
• A connection or component disturbed during recent work can be relevant; the timing of the symptom is evidence, not proof.

A possibility is not a diagnosis. Confirm the cause with the vehicle-specific testing procedure before replacing parts.

Sensible next checks

1. Save other codes and available freeze-frame details. Record whether the rough running occurs cold, warm, at idle or under load.
2. Confirm the cylinder location before any component work. With the engine off and cool, a visual check for a loose connector after recent service is reasonable; do not unplug ignition parts on a running engine.
3. Have the affected cylinder compared with the others using the vehicle-specific ignition, injector and compression tests.

When to get professional help

Request diagnosis if the warning persists or returns. Ask what test identified the cause before approving a coil, injector or mechanical repair.

Related codes

• P0300 — Random/Multiple Cylinder Misfire Detected
• P0302 — Cylinder 2 Misfire Detected
• P0171 — System Too Lean (Bank 1)