OBD codes / P0301
P0301
SeriousCylinder 1 Misfire Detected
Treat P0301 with some urgency. A steady check-engine light with a mild misfire is usually drivable short-term, but a FLASHING light means raw fuel is reaching the catalytic converter and can ruin it — pull over and have it towed or diagnosed. Misfires also tend to worsen, so don't put the fix off.
What this code means
A misfire means a cylinder isn't burning its air-fuel mixture properly. Unlike P0300 (random/multiple), P0301 points to one specific cylinder — number 1 — which actually makes it easier to diagnose. The usual cause is that cylinder's spark plug or ignition coil, and a quick test is to swap the coil or plug with a neighboring cylinder and see if the misfire follows. Less commonly it's a clogged or dead fuel injector, or low compression in that cylinder from a valve or ring problem. Because unburned fuel can overheat the catalytic converter, a steady misfire shouldn't be left for long.
Symptoms you might notice
- Rough idle or shaking, often felt at a stop
- Loss of power or hesitation under acceleration
- Flashing check-engine light during an active misfire
- Reduced fuel economy
- Engine may stumble or be hard to start
What it costs to fix
Typical range: $80–$600 · about ~0.3–3 hrs of labor
| If the cause is… | Part | Labor |
|---|---|---|
| Spark plug (single) | $4–$30 | ~0.3–1.5 hrs |
| Ignition coil (single) | $30–$150 | ~0.3–1 hrs |
| Fuel injector (single) | $100–$400 | ~1–3 hrs |
A single plug or coil is the cheap, common fix; an injector is pricier; low compression (a valve or ring issue) is a major repair that varies too much to quote — get it diagnosed if plug, coil, and injector all check out.
The price swings on which cause it turns out to be — so confirm the cause before paying. Diagnose P0301 for my exact vehicle →
How to fix P0301
Easy — basic tools, most owners can do this
- Locate cylinder 1 on your engine
Cylinder numbering varies by manufacturer — number 1 is at the front of most inline fours, but V6/V8 layouts differ between brands. Confirm the location from a diagram for your engine first; working on the wrong cylinder wastes the whole diagnosis.
- Swap the cylinder 1 coil with a neighbor
Move coil 1 to another cylinder, clear the code, and drive. If the code changes to the other cylinder (say P0303), the coil is bad — replace it. If P0301 stays put, the coil is fine and the fault is in the plug, injector, or cylinder itself.
- Inspect and replace the cylinder 1 spark plug
With the coil out, pull plug 1 and look for a cracked insulator, worn electrodes, oil fouling, or an incorrect gap. A single plug is cheap enough that replacing it while you're in there is almost always worth it.
- Test the cylinder 1 injector
If plug and coil check out, listen to injector 1 with a mechanic's stethoscope for a steady click at idle, or swap it with a neighboring injector and see if the misfire follows. A dead or clogged injector on one hole mimics an ignition fault.
- Run a compression test on cylinder 1
With spark and fuel proven good, thread a compression gauge into hole 1 and compare the reading to the other cylinders. A noticeably low number points to a valve or ring problem — shop territory.
DIY or shop? The coil-swap test, a new plug, and even an injector swap are classic driveway jobs on most engines — coil-on-plug coils come off with one bolt, and the swap test costs nothing. It becomes shop work if compression comes back low, or if cylinder 1 on your particular engine hides under the intake manifold.
Tools for the DIY steps: OBD-II scanner · Spark plug socket · Ratchet and extension · Small socket set for the coil bolt · Compression tester (optional) · Mechanic's stethoscope (optional)
Not sure which step applies to your car? Get the likely cause for your exact vehicle before buying anything for P0301.
P0301 on specific vehicles
The likely causes shift by model. We’ve written up the patterns we see most:
Frequently asked
Can I drive with P0301?
With a steady (not flashing) light and only a mild misfire, short trips are usually fine — but get it looked at soon. If the light is flashing, the active misfire is dumping raw fuel into the catalytic converter and can destroy it; stop driving and have the car towed.
How do I know if it's the coil or the spark plug?
The classic test is to swap cylinder 1's coil (or plug) with a neighboring cylinder and clear the code. If the misfire moves to the other cylinder, the part you moved is the culprit. It's a cheap way to avoid replacing the wrong thing.
How much does it cost to fix P0301?
Often modest — a single spark plug or coil is the common, inexpensive fix. It rises if the cause is a fuel injector, and a compression problem (valve or ring) is a major repair that varies widely. Confirm the cause before spending.
Should I replace all the coils or just cylinder 1?
If only cylinder 1 is misfiring, replacing just its coil/plug is reasonable. Some owners do all of them at once if the parts are old and high-mileage, to avoid chasing the next one — but it isn't required to fix P0301.
Seeing P0301 on your car? Get a diagnosis specific to your exact year, make and model.
Diagnose P0301 for my vehicleSymptoms that trigger P0301
Drivers who get this code often notice one of these — each has its own likely-causes and cost guide:
Related trouble codes
Don’t have a scanner yet? A ~$25 Bluetooth adapter reads codes like P0301 from your phone — see our honest guide to the best OBD2 Bluetooth adapters.
Generic OBD-II reference. Manufacturer-specific behavior varies — confirm with a scan tool and, for safety-related codes, a professional inspection.