P0301 Cylinder 1 Misfire Detected
The PCM has detected a misfire specifically on cylinder 1.
Definition
P0301 means the PCM detected crankshaft speed variations consistent with cylinder 1 not contributing power. The diagnostic path is to verify cylinder 1's spark, fuel, and compression in that order.
Common causes
- Failed spark plug or coil on cylinder 1
- Leaking or clogged fuel injector on cylinder 1
- Low compression on cylinder 1 (burned valve, broken ring)
- Vacuum leak at the cylinder 1 intake runner
- Wiring or connector fault to cylinder 1 coil/injector
Common misdiagnoses
- Replacing all spark plugs and coils when only cylinder 1 components were faulty.
Troubleshooting steps
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1. Swap the cylinder 1 coil with another cylinder
If P0301 changes to a different cylinder code, the coil is bad. If it stays as P0301, the coil is fine.
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2. Inspect the cylinder 1 spark plug
Look for fouling, gap, cracks, or oil contamination.
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3. Test cylinder 1 compression
Low compression points to mechanical issues (rings, valves, head gasket).
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4. Test injector resistance + click
Verify the cylinder 1 injector is firing and not clogged.