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What Is the P0301 Code on a Honda?
The P0301 code means the ECM has detected a misfire specifically in cylinder 1 — either no combustion event occurred, or it was weak enough to cause a noticeable change in crankshaft speed. The ECM identifies which cylinder is misfiring by monitoring tiny fluctuations in crankshaft rotation between firing events.
On Honda models, cylinder 1 misfires are usually traced to ignition components (spark plugs and coils), fuel delivery, or — on newer turbocharged direct-injection engines — carbon buildup on the intake valves.
Common Symptoms
- Check Engine Light, often flashing during an active misfire
- Rough idle or a noticeable shake, especially at idle or low RPM
- Reduced power or hesitation under acceleration
- Increased fuel consumption
- Possible smell of unburned fuel from the exhaust
P0301 Causes on Honda
| Cause | Likelihood | Models Most Affected | Typical Fix Cost |
|---|---|---|---|
| Worn or fouled spark plug (cylinder 1) | Very High | All models | $10–$30 per plug, often replaced as a set |
| Faulty ignition coil (cylinder 1) | High | All models, especially over 80,000 miles | $40–$120 per coil |
| Clogged or faulty fuel injector (cylinder 1) | Moderate | All models | $50–$150 per injector |
| Carbon buildup on intake valves | Moderate | Turbo direct-injection models (1.5L and 2.0L turbo Civic, Accord, CR-V) | $200–$600 for walnut blasting service |
| Vacuum leak near the cylinder 1 intake runner | Lower | All models | $50–$200 |
| Low compression (worn rings or valve issue) | Lower | High-mileage engines | Varies — can be a major repair |
Model-Specific P0301 Notes
8th and 9th Generation Civic (R18, 2006–2015)
On these naturally aspirated four-cylinder engines, P0301 is almost always a spark plug or ignition coil issue. Spark plugs are inexpensive and easy to inspect — look for excessive gap wear, fouling, or oil contamination, which can also point to a valve cover gasket leak dripping oil onto cylinder 1.
10th Generation Civic, Accord, and CR-V (1.5L and 2.0L Turbo, Direct Injection)
Direct-injection turbo engines do not have fuel spraying onto the back of the intake valves to keep them clean, so carbon deposits build up over time and can interfere with airflow and combustion in individual cylinders. If P0301 (or misfires that move between cylinders) appears on one of these engines with no obvious spark or fuel issue, a borescope inspection of the intake valves for carbon buildup is worthwhile before replacing other parts.
Civic Si and Type R (K20C)
These higher-output engines are more sensitive to ignition issues under load. A cylinder 1 misfire that only appears at higher RPM or under boost often points to an ignition coil or spark plug that is marginal but not yet bad enough to misfire at idle.
Diagnostic Steps
- Read all codes and check freeze frame data — note the RPM and engine load when the misfire occurred
- Remove and inspect the spark plug from cylinder 1 for wear, fouling, or oil contamination
- Swap the ignition coil from cylinder 1 with another cylinder’s coil and see if the misfire follows the coil
- Check the fuel injector for cylinder 1 — resistance test or listen for a consistent clicking sound with a mechanic’s stethoscope
- Check for vacuum leaks near the cylinder 1 intake runner using a smoke test or carb cleaner spray method
- On turbo direct-injection engines, consider a borescope inspection of the intake valves for carbon buildup
- If all of the above check out, perform a compression test on cylinder 1 to rule out a mechanical issue
Recommended Scanners for Honda P0301
For misfire codes, the most useful capability is graphing misfire counts per cylinder in live data, and ideally activating individual injectors or coils to isolate the faulty component.
- BlueDriver Bluetooth Pro — shows misfire counts per cylinder and freeze frame data, useful for confirming which cylinder is affected and under what conditions.
- Autel AL619 — solid live data graphing alongside ABS access for other warning lights.
- THINKCAR ThinkDiag 2 — its bidirectional functions can activate individual fuel injectors and ignition coils, making it easier to isolate a cylinder 1 misfire to a specific component without swapping parts.
Related Honda Diagnostic Guides
For our full scanner lineup for Honda-specific codes, see Best OBD2 Scanners for Honda Vehicles. If your Honda is also showing a catalytic converter efficiency code, unresolved misfires are a leading cause — see our Honda/Acura P0420 guide. For EVAP and thermostat-related codes on the same vehicles, see our Honda P1456 and Honda Civic P0128 guides.
Frequently Asked Questions
What does the P0301 code mean on a Honda?
P0301 means the ECM detected a misfire in cylinder 1 — either a missed or weak combustion event — based on small fluctuations in crankshaft speed. On Honda models, it is most often caused by a worn spark plug or failing ignition coil for that cylinder.
How much does it cost to fix P0301 on a Honda?
A spark plug or ignition coil replacement typically costs $10–$120 per part, often done as a set across all cylinders for an even fix. Carbon buildup on turbo direct-injection engines runs $200–$600 for a walnut blasting service, and a failed fuel injector is $50–$150.
Is it safe to drive with a P0301 misfire code?
Driving short distances at low speed is generally not harmful, but a sustained misfire can damage the catalytic converter by sending unburned fuel into the exhaust, and a flashing Check Engine Light specifically warns of an active misfire that should be addressed promptly. Avoid prolonged driving until the misfire is diagnosed.
Can carbon buildup cause P0301 on a Honda?
Yes, on turbocharged direct-injection engines (1.5L and 2.0L turbo Civic, Accord, and CR-V), carbon deposits on the intake valves can disrupt airflow and combustion enough to cause a misfire in one or more cylinders. This is more likely if the misfire moves between cylinders rather than staying fixed on cylinder 1.
Why does the misfire only happen on cylinder 1 and not other cylinders?
Each cylinder has its own spark plug, ignition coil, and fuel injector, so a fault in any one of those parts will cause a misfire isolated to that cylinder. Cylinder 1 is not inherently more failure-prone than the others — it simply happens to be the cylinder where a worn part currently exists.
