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 →
How to fix P0307
Moderate — doable at home with common tools and patience
- Map out cylinder 7 on your V8
A P0307 means you're working on an engine with at least seven cylinders — almost always a V8, where numbering differs sharply between brands (GM, Ford, and European makers all count differently). Confirm cylinder 7's bank and position from a diagram before pulling anything.
- Exchange coil 7 with another cylinder
Swap the cylinder 7 coil with one from the opposite bank or a neighboring cylinder, clear the code, and drive. The misfire following the coil to its new cylinder is a definitive coil verdict; staying on 7 exonerates it.
- Read and replace spark plug 7
Pull the plug and inspect it — oil fouling, a bridged gap, or worn electrodes each tell their own story about why cylinder 7 is missing. On a V8 at plug-change mileage, budget for the full set rather than chasing plugs one at a time.
- Check injector 7's operation
Listen for a consistent click from injector 7 at idle, or measure its resistance against a healthy sibling. On direct-injection V8s the injectors are harder to access and swap, so resistance testing is the practical first check.
- Compression-test cylinder 7 if the misfire persists
With spark and fuel verified, a lingering P0307 calls for a compression reading on that hole. A weak cylinder needs a leak-down test to say whether it's valves, rings, or a head gasket — a diagnosis worth paying a shop for.
DIY or shop? Plug and coil work on many pickup and rear-drive V8s is straightforward DIY since the engine sits longitudinally with both banks reachable. It shifts to shop territory on tightly packaged engine bays, on direct-injection engines where injector service needs special tools, and whenever compression testing points to an internal problem.
Tools for the DIY steps: OBD-II scanner · Spark plug socket (5/8 in or 14mm as fitted) · Ratchet with extensions · Multimeter · Dielectric grease · Torque wrench
Not sure which step applies to your car? Get the likely cause for your exact vehicle before buying anything for P0307.
P0307 on specific vehicles
The likely causes shift by model. We’ve written up the patterns we see most:
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 vehicleRelated trouble codes
Don’t have a scanner yet? A ~$25 Bluetooth adapter reads codes like P0307 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.