P0301 — Misfire in cylinder 1 — engine loses grunt, hesitates under acceleration, shakes at idle, fuel economy worsens

What it means

Common causes

• Cylinder 1 spark plug worn, oil-fouled, cracked insulator, or wrong gap
• Cylinder 1 ignition coil — common failure with age or heat
• Cylinder 1 injector — clogged, leaking, or won't hold pressure (test on a bench)
• Loss of compression in cylinder 1: burnt valve, cracked ring, holed piston
• Damaged wiring or rotted connector to cylinder 1 coil/injector
• Very local vacuum leak into cylinder 1 — rare but possible cracked runner
• Burnt exhaust valve in cylinder 1 — often after running lean for a long time

How to diagnose

1. 01

   Read all stored and pending codes with an OBD-II adapter — get the full picture, not just the one code.

2. 02

   Capture freeze-frame data (RPM, coolant temperature, engine load) at the exact moment the code triggered.

3. 03

   Inspect the named subsystem with our app's AI explanation — get vehicle-specific causes for your make, model and year.

Related codes

• P0300 Random misfire across multiple cylinders — engine shakes at idle, stumbles under load, loses power, Check Engine light on solid or flashing
• P0302 Misfire in cylinder 2 — same diagnosis as P0301 but on cylinder 2. Rough running, power loss
• P0303 Misfire in cylinder 3. Consistent engine shake, most noticeable on cold start
• P0304 Misfire in cylinder 4. Often shows up alone on 4-cylinder engines due to uneven plug wear
• P0305 Misfire in cylinder 5. Applies to 5/6/8-cylinder engines (V6, inline-5, V8)
• P0306 Misfire in cylinder 6. On V6 this is the last cylinder — often wears first due to heat exposure