An engine misfire at highway speed on your 2016 Nissan Altima with code P0301 indicates cylinder 1 is not firing properly under load. Misfires that appear specifically at highway speeds often point to causes that only manifest when the engine is working harder.
Understanding P0301
Code P0301 indicates the engine computer has detected misfire specifically in cylinder 1. When this occurs primarily at highway speeds, it suggests the ignition or fuel system can't keep up with higher load demands. The cylinder may fire adequately at idle but fail under acceleration or sustained high-speed driving.
Load-Related Misfire Causes
Misfires that appear under load typically result from weak ignition coil that fails when hot or under demand, spark plug with worn electrode unable to fire under compression, fuel injector not delivering adequate fuel at higher RPM, low fuel pressure unable to maintain mixture under load, and compression loss in the affected cylinder.
Diagnostic Process
Start with cylinder 1 spark plug inspection - check gap, electrode wear, and insulator condition. Test the ignition coil on cylinder 1 with an ohmmeter and compare to specifications. Swap the coil with another cylinder to see if the misfire follows. Check fuel injector operation and fuel pressure under load conditions.
Additional Tests
A compression test on cylinder 1 can reveal mechanical issues affecting that cylinder. Compare compression readings across all cylinders. Low compression in cylinder 1 points to valve, head gasket, or ring issues. Some shops perform leak-down testing for more detailed diagnosis.
Common Repairs
Many highway-speed misfires resolve with ignition coil replacement on the affected cylinder. Spark plugs should be replaced with proper gap setting. If fuel delivery is the issue, injector cleaning or replacement may be needed. Mechanical issues like low compression require more extensive repair.