P0301 cylinder 1 misfire explained: likely ignition, injector and compression causes, useful swap tests and when a flashing engine light makes the fault more urgent.
Diagnose promptly to protect the catalyst
P0301 means the ECU has repeatedly detected a misfire associated with cylinder 1. The code identifies the affected cylinder, but it does not identify the failed component.
No. A coil is a common suspect on coil-on-plug petrol engines, but the plug, injector, wiring, intake sealing and mechanical compression can create the same cylinder-specific code. The code tells you where to investigate, not which part to order.
Where the vehicle design allows it, a technician may compare or swap ignition components between cylinders and see whether the misfire follows the component. Injector testing, compression testing and smoke testing for intake leaks can then investigate faults that stay on cylinder 1.
A flashing malfunction indicator can accompany a severe active misfire. Unburnt fuel entering the exhaust can overheat the catalytic converter, so reduce engine load and avoid continuing to drive a badly shaking vehicle.
Note whether the misfire is worse cold or hot, at idle or under load, and after wet weather or refuelling. Freeze-frame data and any companion codes can make those observations much more useful.
AutoAid can consider P0301 alongside the vehicle, symptoms and follow-up answers. That is more useful than treating the code as a replacement-parts instruction.
Start guided diagnosisSAE J2012 defines the diagnostic trouble-code format used for generic OBD codes. AutoAid's live reference layer uses the open OBDex generic-code dataset. Manufacturer-specific codes and test procedures should be checked against the vehicle maker's technical information.
AutoAid provides AI-assisted guidance only and never a guarantee. All faults, urgency ratings and prices are estimates — a physical inspection by a qualified mechanic may still be required.