OBD-II Car P0301 Error
What it means
P0301 means the engine computer has detected a misfire in cylinder #1 — the combustion in that specific cylinder is failing to complete properly, either because of weak spark, wrong fuel delivery, or a mechanical problem. The computer watches the crankshaft speed and notices when cylinder #1 is not contributing its normal power. Common symptoms are a rough or shaking idle, hesitation and poor acceleration, a noticeable loss of power, engine knocking sounds, reduced fuel economy, and a check engine light that may flash. A flashing check engine light is important: it means the misfire is severe enough to dump raw fuel into the exhaust and damage the catalytic converter, so you should stop driving and shut the engine off when it flashes.
The bottom line on the P0301 error
P0301 isolates the misfire to cylinder #1, and the usual culprit is a worn spark plug or a failing ignition coil, making it DIY-friendly. The trap is driving on: a flashing check engine light means raw fuel is hitting the exhaust and can ruin the catalytic converter, so shut the engine off.
Start cheap — swap the #1 coil with a neighbor and clear the code; if the misfire jumps to P0302, the coil is bad. A plug is $10–$40 and a coil $80–$300 installed, so it stays a repair unless a compression test reveals a valve or head-gasket fault.
P0301 snapshot
Our own at-a-glance triage of the P0301 error, from the verified data on this page. See error-code rankings → · How we score →
Common causes of the P0301 error
- Worn or fouled spark plug in cylinder #1
- Faulty ignition coil or coil pack feeding cylinder #1
- Clogged, leaking, or dead fuel injector on cylinder #1
- Vacuum leak near cylinder #1 causing a lean misfire
- Low compression from a leaking valve, worn rings, or a head gasket issue in cylinder #1
- Damaged or carbon-tracked spark plug wire (on engines that use wires)
- Faulty sensor or wiring causing incorrect spark/fuel timing for that cylinder
Which OBD-II cars get the P0301 error
P0301 is universal on OBD-II vehicles (1996+) and pinpoints cylinder #1 specifically. It is most common on coil-on-plug engines past 60,000–100,000 miles — frequently seen on Honda/Acura, Toyota/Lexus, Ford, and GM four- and six-cylinders, where a single worn plug or a failing coil on the #1 cylinder is the usual culprit.
How to fix the OBD-II Car P0301 error
- 1Swap and inspect the spark plug and coil for cylinder #1Pull the cylinder #1 spark plug and check for fouling, cracks, or wear, and replace if needed. A quick diagnostic trick is to swap the cylinder #1 ignition coil with a neighboring cylinder's coil and clear the code: if the misfire follows the coil to the new cylinder (e.g. becomes P0302), the coil is bad. Cylinder #1 location varies by engine — confirm it before working.
- 2Test or swap the fuel injectorIf the plug and coil are good, check the cylinder #1 fuel injector. Listen for its clicking with a mechanic's stethoscope, check its electrical signal, and swap it with an adjacent injector to see if the misfire moves. A clogged injector can be cleaned, but a dead one needs replacement.
- 3Check for vacuum leaks and intake problemsA vacuum leak near cylinder #1 leans out that cylinder and causes a misfire. Inspect intake gaskets, hoses, and the PCV system for cracks or loose connections, and clear any accompanying lean codes (P0171/P0174) first.
- 4Perform a compression test if spark and fuel are fineIf ignition and fuel both check out and the misfire persists, do a compression (and ideally a leak-down) test on cylinder #1. Low compression points to a mechanical fault — a burned valve, worn rings, or a head gasket leak — which is a more involved repair.
🧰 When to call a professional
Call a professional if the check engine light is flashing, if the misfire persists after replacing the plug, coil, and injector for cylinder #1, or if a compression test shows low compression (a mechanical problem). Do not keep driving with a flashing light, as an unburned-fuel misfire can quickly destroy the catalytic converter, which is far more expensive than the original repair.
OBD-II P0301 vs OBD-II P0300 vs OBD-II P0303: how they compare
How this code stacks up against related error codes for difficulty, urgency, and cost.
| OBD-II P0301 | OBD-II P0300 | OBD-II P0303 | |
|---|---|---|---|
| DIY difficulty (1–5) | 3 | 3 | 3 |
| Urgency (1–5) | 4 | 4 | 4 |
| Typical cost | $$ | $$ | $$ |
How much does it cost to fix the P0301 error?
| DIY parts only | $10–$300 |
| Professional diagnosis & repair | $100–$500 |
| If major component (low compression / valve) | $1,000–$3,000+ |
Repair or replace?
P0301 is usually a cheap-to-moderate fix because it isolates one cylinder, so you replace only that cylinder's plug ($10–$40) or coil ($80–$300 installed) rather than a full set. This is one of the most DIY-friendly codes: swap the #1 coil with a neighboring cylinder and clear the code — if the misfire moves (to P0302), you have found a bad coil for a few dollars of diagnosis. Pay a shop when a compression or leak-down test is needed, which points to a burned valve, worn rings, or a head gasket ($1,000+). Never keep driving with a FLASHING check engine light — a sustained single-cylinder misfire pumps raw fuel into the exhaust and can ruin the catalytic converter, which costs far more than the coil that caused it.
Common replacement parts for the P0301 error
| Spark plug (cylinder #1) | $10–$40 | Cheapest fix; inspect for fouling or wrong gap | |
| Ignition coil (cylinder #1) | $80–$300 | Installed; swap-test to confirm before buying | |
| Fuel injector (cylinder #1) | $150–$500 | If plug and coil are good; clean or replace |
Prices are typical retail ranges and vary by model and supplier — always confirm the exact part number for your appliance before buying.
OBD-II P0301 error — FAQ
＋ − Is it safe to drive with this code?
It depends. If the check engine light is steady and the engine runs only slightly rough, you can usually drive a short distance to a shop. But if the light is FLASHING, stop driving as soon as it is safe — a flashing light signals an active, severe misfire that can overheat and ruin the catalytic converter. A long-term misfire also risks further engine damage.
＋ − How much does it cost to fix?
It depends on the cause. A spark plug is cheap ($10–$40), and an ignition coil typically runs $80–$300 installed. A fuel injector replacement is often $250–$500. If the misfire is mechanical (low compression from valves, rings, or a head gasket), repairs can run from several hundred to a few thousand dollars. Start with the cheapest likely causes — plug and coil — first.
＋ − What does the '1' in P0301 mean?
The last digit identifies the cylinder that is misfiring — P0301 is cylinder #1, P0302 is cylinder #2, and so on. A P0300 code (with a zero) means a random or multiple-cylinder misfire rather than a single identified cylinder. Knowing the exact cylinder lets you focus your diagnosis on that one spark plug, coil, and injector.
Sources & manufacturer references
This guide is independently written and not affiliated with OBD-II. Always unplug appliances before servicing and follow your model's manual. Error codes and steps can vary by model — when in doubt, consult a qualified technician.