P0301
High SeverityCylinder 1 Misfire Detected
Ignition System
What Does P0301 Mean?
Cylinder 1 is misfiring — not firing properly. Could be spark plug, coil, injector, or compression issue on that specific cylinder.
Common Fix
Replace spark plug or ignition coil on cylinder 1
Estimated Cost (DIY)
$5 - $80
Symptoms
- ⚠️Rough idle
- ⚠️Loss of power
- ⚠️Check engine light (may flash)
- ⚠️Vibration
Common Causes
Bad spark plug on cylinder 1likely
Faulty ignition coil on cylinder 1likely
Bad fuel injectorpossible
Low compression (valve or gasket)possible
How to Diagnose P0301
- 1Swap spark plug with known good cylinder — see if misfire moves
- 2Swap coil with another cylinder — see if code follows
- 3Check injector operation
- 4Run compression test if spark and fuel are good
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Frequently Asked Questions
- How do I find cylinder 1?
- Cylinder 1 location varies by engine. Check your repair manual. On most inline engines, it is at the front (belt end).
- Can I just replace one spark plug?
- You can, but it is recommended to replace all plugs at the same time since they wear together.