Trouble codes › P0301

P0301 Cylinder 1 Misfire Detected

Ignition and misfire

P0301 means cylinder 1 is misfiring, usually from a bad spark plug, ignition coil or fuel injector on that cylinder.

The engine computer has seen cylinder 1 fail to fire often enough to set a code. Cylinder 1 is the one the engine's maker numbers first; where it sits depends on the engine. The same check covers every cylinder: P0302 is cylinder 2, P0303 cylinder 3, and so on.

Can I keep driving? Not if you can avoid it.

If the check-engine light is flashing, stop driving as soon as you safely can to protect the catalytic converter. With a steady light and a mild miss, drive gently and get it fixed soon.

Common causes

  1. A worn or fouled spark plug in cylinder 1
  2. A failing ignition coil or plug wire on cylinder 1
  3. A clogged or leaking fuel injector on cylinder 1
  4. A vacuum leak near cylinder 1's intake runner
  5. Low compression in cylinder 1: a burnt valve, worn rings or head gasket (less common)

Symptoms

  • Rough idle or a steady shake
  • Loss of power, hesitation
  • Flashing or steady check-engine light

Known problems: GM V8 AFM/DFM lifter failure · 5.7L Hemi lifter and camshaft wear ("Hemi tick") · Honda 3.5L V6 VCM misfires and fouled spark plugs

What to check first

  1. Find cylinder 1 for your engine (your service information or an owner forum).
  2. Swap the cylinder 1 ignition coil with a neighboring cylinder, clear the code and drive. If the misfire moves to that cylinder (for example P0302), the coil is bad.
  3. Pull and inspect the spark plug: oil, heavy carbon, a cracked insulator or a worn gap all point to the cause.
  4. If the coil and plug are fine, swap injectors or have the injector tested, and check for vacuum leaks near that cylinder.
  5. Still misfiring? A compression or leak-down test tells you whether it's mechanical.

What does P0301 mean on your vehicle?

The likely cause depends on your engine. iRepair researches your exact year, make, model and engine (service bulletins, recalls and owner reports) and tells you what to check first. Your first 3 questions are free.

Ask iRepair about P0301

No scanner? Most auto parts stores read check-engine codes for free.

Related codes

General guidance for P0301 on most vehicles. Some makers use the same code a little differently; confirm in the service information for your vehicle, put safety first, and see a professional when in doubt.