Code
P0301
Ignition / Engine
Cylinder 1 misfire detected
Cylinder 1 is not firing correctly. Swapping parts isolates the cause.
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Most likely causes
- Faulty spark plug or coil on cyl 1
- Injector fault on cyl 1
- Vacuum leak on runner 1
- Low compression cyl 1
Symptoms you may notice
- Rough idle
- Shaking under load
- Check engine light
Checks to run
- Swap coil/plug to another cylinder and watch the code move
- Inspect the plug
- Test the injector
- Compression test
Tools you may need
OBD-II scanner
Spark plug socket
Multimeter
Compression tester
Always diagnose before replacing. Codes share symptoms; confirm the cause with measurements before buying parts.