P0301 P0xxx · Powertrain (P) High severity
Cylinder 1 Misfire Detected
Cylinder 1 is not contributing power consistently. Unlike a random misfire, this is isolated to one cylinder — so swap-testing parts will find it fast.
Severity guidance: High — stop driving and diagnose now; risk of further damage
Symptoms you will notice
- Shaking at idle
- Flashing check-engine light under load
- Fuel smell
- Loss of power
Common causes
Ordered from most to least likely — start at the top.
- 1 Worn or fouled spark plug
- 2 Failed ignition coil
- 3 Faulty injector
- 4 Low compression from a burnt valve or worn rings
- 5 Intake leak at that cylinder's runner
How to diagnose it
Cheapest and least invasive first — most of these codes are not a parts problem.
- ✓ Read the misfire counter per cylinder to confirm it really is cylinder 1 and not a general misfire.
- ✓ Swap the coil and plug with another cylinder — if the misfire moves, you have your answer.
- ✓ Swap the injector next if ignition parts test good.
- ✓ Run a compression and leak-down test if the misfire stays on cylinder 1.
Repair options
- Replace plugs and/or coil
- Replace or clean the injector
- Valve or piston repair if compression is low
P0301 — frequently asked questions
Why does the light flash? +
A flashing MIL means catalyst-damaging misfire. Stop and fix it — do not drive through it.
Is it always the coil? +
No. Work through ignition → fuel → compression; guessing costs more than testing.
Confirm the diagnosis before you buy parts
Send us the code, freeze-frame data and the vehicle — our engineers will tell you what to test first.