P0304 — Misfire in cylinder 4. Often shows up alone on 4-cylinder engines due to uneven plug wear

What it means

Common causes

• Cylinder 4 spark plug worn
• Cylinder 4 ignition coil (on 4-cylinders — farthest from battery)
• Cylinder 4 injector — often the last to clog in a row
• Cylinder 4 compression — burnt valve
• Wiring to cylinder 4 — often the longest run and most heat-exposed
• Intake manifold leak near cylinder 4
• Sometimes cylinder head warping affects cylinder 4 first on 4-cyls

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