P0301
P0301 Cylinder 1 Misfire
P0301 means the engine computer detected repeated misfires on cylinder 1. Because it names one cylinder, diagnosis usually starts by comparing cylinder 1 ignition, fuel, and compression against the other cylinders.
How urgent is P0301?
Do not ignore a cylinder-specific misfire, especially if the light flashes. Raw fuel can damage the catalytic converter.
Common symptoms
- Rough idle
- Shaking
- Poor acceleration
- Check engine light
- Fuel economy drop
Likely causes
- Bad cylinder 1 spark plug
- Bad cylinder 1 ignition coil
- Injector issue
- Vacuum leak near cylinder 1
- Compression problem
What to check before replacing parts
1
Swap the coil with another cylinder and see if the code follows
2
Inspect the spark plug
3
Check injector pulse and flow
4
Look for intake leaks
5
Test compression on cylinder 1
Use the code with symptoms
A code points at the system, not always the failed part. Add your vehicle, mileage, symptoms, and whether the check engine light is steady or flashing so the AI diagnostic can narrow the next step.