What does P0301 mean?
P0301 indicates that the engine control system has detected a misfire on cylinder 1.
Unlike P0300, which indicates random or multiple-cylinder misfires, P0301 points the diagnostic process toward a specific cylinder.
Possible symptoms
- Rough idle
- Engine vibration
- Loss of power
- Hesitation during acceleration
- Poor fuel economy
- Check engine light
- Hard starting in some cases
Common causes
- Faulty spark plug
- Faulty ignition coil
- Injector problem
- Injector wiring fault
- Vacuum leak near the affected cylinder
- Low compression
- Valve or mechanical engine problem
- Incorrect fuel mixture
A useful diagnostic strategy
If the vehicle uses interchangeable ignition coils, a technician may test whether the misfire follows the coil when it is moved to another cylinder. Similar testing can sometimes be used with other components, depending on the vehicle.
Electrical tests, injector checks, compression testing, and scan data can help separate an ignition, fuel, wiring, or mechanical problem.
Do not replace parts based only on P0301
The code identifies the cylinder where the misfire was detected. It does not automatically prove which component caused the misfire.