OBD codes / P0307
P0307
SeriousCylinder 7 Misfire Detected
Treat P0307 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. P0307 points to one specific cylinder — number 7 — which makes it easier to diagnose than a random misfire. The usual cause is that cylinder's spark plug or ignition coil; 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 P0307 for my exact vehicle →
Frequently asked
Can I drive with P0307?
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?
Swap cylinder 7'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 — a cheap way to avoid replacing the wrong thing.
How much does it cost to fix P0307?
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 7?
If only cylinder 7 is misfiring, replacing just its coil/plug is reasonable. Some owners replace 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 P0307.
Seeing P0307 on your car? Get a diagnosis specific to your exact year, make and model.
Diagnose P0307 for my vehicleGeneric OBD-II reference. Manufacturer-specific behavior varies — confirm with a scan tool and, for safety-related codes, a professional inspection.