P0301 means Cylinder 1 Misfire Detected. It identifies the cylinder with a detected combustion problem, not the part to replace. Confirm where cylinder 1 is on your engine, save the scan evidence, and investigate ignition, fuel delivery, air leaks and mechanical condition in a controlled sequence.
If you have already installed a spark plug or coil and P0301 returns, changing another part is not the most useful next step. The next step is to find out whether the fault stayed with the cylinder, followed a component, or appears only under particular conditions.
Flashing light or severe shaking? Reduce load, pull over safely and stop the engine when safe. Continued misfiring can overheat the catalytic converter. Arrange assistance if the engine shakes badly, stalls, smells strongly of raw fuel or loses substantial power.
First, identify the correct cylinder
Cylinder 1 is not always the first cylinder you see when opening the hood. Engine orientation and numbering vary. Use the diagram for your exact engine; do not infer the location from left/right descriptions in an unrelated video.
P0300 describes random or multiple-cylinder misfire, while P0301 identifies cylinder 1. Both may appear in the same scan. If several cylinders are involved, widen the investigation to shared air, fuel or mechanical causes instead of treating every coil as a separate failure. Our P0300 guide covers that broader pattern.
Record the pattern before touching parts
| What to save | Why it helps |
|---|---|
| All codes and statuses | An injector-circuit, ignition-circuit or fuel-trim fault can change the test order. |
| Freeze-frame RPM, load and coolant temperature | Distinguishes a cold-start event from a warm-idle or loaded-engine event. |
| When the symptom occurs | A repeatable trigger is more useful than “it sometimes runs badly.” |
| Cylinder-specific misfire counts, if supported | Shows whether cylinder 1 continues accumulating events under a controlled check. |
| Recent plugs, coils, intake work or washing | Directs attention to disturbed connectors, incorrect parts, leaks or moisture. |
Misfire counters are not available through every vehicle/tool combination. An empty or unsupported data field does not establish that the cylinder is healthy. Use the codes, symptoms and appropriate tests together.
Check accessible ignition components first
With the ignition off and engine cool, inspect the cylinder 1 connector, accessible wiring and coil seating. If you are qualified to remove the coil and plug using the service procedure, look for damaged boots, carbon tracks, moisture, oil in the plug well or a cracked plug insulator.
Confirm the plug type and installation requirements. A new part can still be incorrect, damaged during fitting or affected by an unresolved leak. Oil in a plug well should prompt investigation of its source; replacing a wet coil without addressing the oil does not complete the job.
Do not disconnect ignition components while the engine is running to “see whether the sound changes.” Use the prescribed test method and keep hands away from moving parts and high-voltage ignition components.
How to interpret a coil swap
On a gasoline engine with accessible, interchangeable individual coils, a controlled coil swap can help isolate the cause. Only use this method where service information permits it. Label the original locations, move one component at a time with the engine off, and reconnect everything correctly.
For example, if the cylinder 1 coil is moved to cylinder 2, a newly occurring P0302 or corresponding live misfire pattern supports further investigation of that coil. This is an illustrative test outcome, not a test we performed on an EDIAG vehicle.
| Result after a valid controlled test | What it supports | Next step |
|---|---|---|
| Misfire moves with the coil | A fault associated with the moved coil or boot | Inspect and confirm that component before replacement. |
| Misfire stays at cylinder 1 | The coil swap did not isolate the cause | Check the plug, connector, injector and mechanical condition. |
| No misfire occurs during the recheck | The original operating condition may not have returned | Compare the test conditions with the original freeze frame. |
| Several cylinders now misfire | A connection or shared fault needs review | Recheck assembly and broaden diagnosis before more swaps. |
A coil pack serving several cylinders, an inaccessible installation or a diesel engine requires a different approach. The purpose of the test is to isolate one variable, not to turn component swapping into a repair strategy.
P0301 after new plugs and coils: what comes next?
Recheck the work before assuming a deeper failure: the correct cylinder, correct parts, fully seated connectors and undamaged boots. Then follow the remaining evidence. A cylinder-specific intake leak, injector fault, damaged wiring or reduced compression can all keep the same cylinder misfiring.
Injector electrical and delivery tests, compression testing and leak-down testing answer different questions. A technician can select the next test from the symptom and accompanying codes. Avoid opening high-pressure fuel lines or attempting improvised injector tests; the scan is the starting point for a proper test procedure.
Bring a concise history to the workshop: when P0301 occurs, which parts were changed, what moved during a controlled test and whether the same fault returned. That is more actionable than a list of parts suggested by a generic code lookup.
Verify the repair under the relevant conditions
After the confirmed repair, compare operation with the original complaint: cold start, warm idle or another safely reproducible condition. Check for returning faults and available misfire counts. Keep the original scan and the result after repair with the service record.
If the light is off but the engine still shakes, continue diagnosis. If the engine feels normal but P0301 returns, use the recorded operating conditions to investigate the intermittent fault. Neither the warning light nor a short smooth idle is a complete test on its own.
Common P0301 questions
Does P0301 mean I need four new coils?
No. It identifies a detected misfire at cylinder 1. Test the cause and follow any vehicle-specific replacement recommendations; the code alone does not justify replacing every coil.
Can an injector cause P0301?
Yes. A fuel-delivery or injector-control problem can affect one cylinder. Injector testing should follow the correct electrical and fuel-system procedures.
Why is there no obvious shaking?
The misfire may be intermittent or occur under a condition you are not currently reproducing. Preserve freeze frame and check the fault status.
Should I clear the code before diagnosis?
Save the codes and freeze frame first. A controlled test may later require clearing according to the service procedure, but repeated resets erase useful context.
Reference notes
- EDIAG Elite: codes, freeze frame and live data
- Manufacturer misfire bulletin: an example of vehicle-specific diagnostic paths, not a universal repair instruction
Technical and product information checked September 18, 2026. Use the service procedure for your exact vehicle when testing or repairing a system.
