P0301 Check Engine Code

What's going on

P0301 means the computer detected repeated misfires on cylinder 1 specifically. Unlike P0300 (random/multiple), P0301 points to one cylinder — usually ignition (plug, coil, boot) or injector on that hole. A flashing light with P0301 still risks catalytic converter damage from unburned fuel.

Symptoms

• Check engine light — may flash under load with active misfire
• Rough idle or stumble you can feel at low speed
• P0301 alone or with P0300
• Recent tune-up where cylinder 1 plug or coil was disturbed
• Fuel trim normal or lean on bank including cylinder 1

Common causes

• Failed coil-on-plug or spark plug on cylinder 1
• Cracked plug insulator or wrong plug gap
• Injector restriction on cylinder 1
• Low compression on cylinder 1 (after ignition ruled out)
• Vacuum leak affecting cylinder 1 runner on some intakes

Often sounds like

• P0300 random misfire — multiple cylinders or unstable counts
• P0302–P0308 — other cylinders; swap test isolates if coil-related

How we check it

1. 1 Confirm misfire counts on cylinder 1 with scan tool
2. 2 Inspect plug and coil; swap coil test when safe and applicable
3. 3 Injector and compression tests when ignition is good

What happens next when you bring it in?

1. 1 Call with whether the light flashes and whether roughness is constant or only when cold.
2. 2 We isolate cylinder 1 on scan data before quoting plugs, coils, or deeper work.

Questions we get a lot

What does P0301 mean?

P0301 is “Cylinder 1 Misfire Detected.” The engine computer counted enough misfire events on cylinder 1 to store a code.

Can I swap the coil to test P0301?

On some engines, moving the coil to another cylinder and watching misfire counts move with it speeds diagnosis. We do that when the design allows — instead of guessing at parts.

Is P0301 an emergency?

A steady light with mild roughness — get it scanned soon. A flashing light means active misfire under load; ease off the throttle and come in quickly to protect the catalytic converter.

Related problems

• P0300 Check Engine Code
• Rough Idle
• Check Engine Light