P0301: Cylinder 1 Misfire Detected
TL;DR
P0301 = misfire on cylinder 1 only. Severity: high. STOP driving if the check engine light is flashing. Top causes: bad spark plug (35%), failing coil on cyl 1 (30%), injector/compression (25%). The isolated cylinder makes it easy to swap-test parts. Fix: $20–$250 DIY.
Can I keep driving with P0301?
IF the check engine light is FLASHING → stop driving; a steady misfire dumps raw fuel into the exhaust and overheats the catalytic converter. IF the light is steady → drive only as far as needed to reach help and diagnose promptly.
Symptoms
- Engine shaking, worst at idle
- Check engine light (steady or flashing)
- Loss of power and hesitation
- Rough idle
- Slight fuel smell or poor economy
Top causes (ranked by probability)
| Likely cause | Probability | Notes |
|---|---|---|
| Worn or fouled spark plug (cylinder 1) | 35% | |
| Failing ignition coil on cylinder 1 | 30% | Swap-test with a neighbor |
| Faulty/clogged fuel injector (cylinder 1) | 20% | |
| Low compression / mechanical fault in cylinder 1 | 15% | More serious |
What does P0301 mean?
Technical explanation
The ECM detects crankshaft deceleration during cylinder 1’s power stroke and sets P0301 (the last digit identifies the cylinder). Because the fault is cylinder-specific, the cause is almost always a component serving that cylinder: spark plug, ignition coil, fuel injector, or a mechanical issue such as a leaking valve or low compression in cylinder 1.
In simple terms
Your engine has several cylinders that fire in turn. P0301 means cylinder number 1 is the one misbehaving — it’s not firing cleanly. Since it’s just one cylinder, you can often find the bad part by swapping it with a neighbor and seeing if the problem moves.
How to diagnose P0301 (step by step)
- Check for a flashing light. Flashing = active converter-damaging misfire. Stop and diagnose first.
- Locate cylinder 1. Confirm which cylinder is #1 for your engine (varies by manufacturer) before touching parts.
- Swap the coil. Move cylinder 1’s coil to another cylinder. If the misfire follows the coil, the coil is bad.
- Inspect the spark plug. Check plug 1 for wear, fouling, oil or cracks. Replace if suspect.
- Test injector and compression. If ignition is good, check the injector and run a compression test on cylinder 1.
Repair options & cost
- Replace the spark plug on cylinder 1 (often the whole set)
- Replace the ignition coil on cylinder 1
- Clean or replace the cylinder 1 injector
- Address mechanical issues (valves, compression) if found
| DIY cost | $20–$250 |
|---|---|
| Workshop cost | $100–$450 |
| Repair time | 20–60 min for plug/coil; longer for injector or mechanical work |
Costs are local ballpark ranges and vary by region and vehicle.
Tools you’ll need
- OBD-II scanner (BlueDriver / ANCEL)
- Spark plug socket + gap gauge
- Compression tester
Vehicle-specific notes
- Cylinder numbering differs by engine — verify before swapping parts.
- Coil-on-plug engines: the swap test is the fastest, cheapest confirmation.
- If P0301 keeps returning after parts, suspect a mechanical/compression issue.
Common mistakes to avoid
- Driving with a flashing light and ruining the catalytic converter
- Replacing all coils instead of swap-testing the one on cylinder 1
- Assuming the wrong cylinder is #1 and replacing the wrong parts
- Ignoring a returning code that points to compression loss
Frequently asked questions
What does P0301 mean?
It means cylinder number 1 is misfiring — not burning fuel correctly. The last digit of the code identifies the affected cylinder.
Can I just replace the coil for P0301?
Often yes, but confirm first by swapping cylinder 1’s coil to another cylinder. If the misfire moves with it, the coil is the culprit.
Is P0301 safe to drive with?
Only briefly, and not at all with a flashing light. A sustained misfire can quickly damage your catalytic converter.
How do I find cylinder 1?
Cylinder numbering varies by engine and manufacturer. Check a diagram for your specific engine before replacing parts.
P0301 summary
| Meaning | Cylinder 1 misfire |
|---|---|
| Severity | High |
| Safe to drive? | No if flashing; caution if steady |
| Top cause | Bad spark plug (35%) |
| DIY cost | $20–$250 |
| Shop cost | $100–$450 |