P0301: Cylinder 1 Misfire Detected

What it means

Misfires concentrated on cylinder 1. A cylinder-specific code points away from shared causes (fuel pressure, MAF) toward components dedicated to that cylinder — coil, spark plug, injector, compression.

At a glance

• Usually lights the check-engine light
• Affects emissions; the car can fail an emissions test

How it works

The engine control module uses crankshaft speed changes to judge whether each cylinder is contributing power. P0301 sets when the misfire monitor repeatedly identifies cylinder 1 as having weak or missing combustion.

Common causes

Most likely first.

1. Ignition coil for cylinder 1 failed
2. Spark plug for cylinder 1 worn or fouled
3. Cylinder 1 injector clogged
4. Low compression on cylinder 1

Symptoms

• Check engine light on or flashing
• Rough idle and uneven running
• Power loss, hesitation under acceleration
• Increased fuel consumption
• Possible smell of unburned fuel from exhaust

How to diagnose it

1. Read freeze-frame data and cylinder misfire counters to confirm that cylinder 1 is the one misfiring and note the engine conditions.
2. Inspect cylinder 1's spark plug and ignition coil, including the connector and wiring, for wear, fouling, damage, or a poor connection.
3. If the ignition design allows it, swap cylinder 1's coil with another cylinder and check whether the misfire moves.
4. Check cylinder 1's injector connector and wiring, then test injector operation and fuel delivery using the manufacturer's procedures.
5. If the misfire stays on cylinder 1, test its compression and mechanical condition against the manufacturer's specification.

Common fixes

• Replace a worn or fouled cylinder 1 spark plug.
• Repair a loose or damaged cylinder 1 ignition connection.
• Replace the cylinder 1 ignition coil if the misfire follows it during a swap test.
• Clean or replace the cylinder 1 injector if testing confirms restricted or faulty delivery.
• Repair cylinder 1's mechanical fault if compression testing identifies one.

Can I keep driving?

If the check engine light flashes, stop driving as soon as it is safe; a cylinder 1 misfire can send unburned fuel into the exhaust and damage the catalytic converter. If the light is steady and the engine runs smoothly, limit driving and avoid heavy acceleration until diagnosed.