P0307 code: Cylinder 7 Misfire Detected
P0307 means cylinder 7 Misfire Detected. The code says where to look, not what failed — the fix depends on which cause your car actually has.
What P0307 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.
P0307 symptoms
- 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 P0307
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.
Start a case with P0307 and your car. Redline weighs these causes against what your car shows, and names the check that would settle it before you buy parts.
Can I drive with P0307?
Redline can’t determine from a symptom or code alone whether your car is safe to drive.
P0307 on specific vehicles
The likely causes shift by model. We’ve written up the patterns we see most:
P0307: common questions
Can I drive with P0307?
A misfire code alone doesn't settle that. With a steady (not flashing) light, 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.
Related trouble codes
Don’t have a scanner yet? A ~$25 Bluetooth adapter reads codes like P0307 from your phone. See our guide to the best OBD2 Bluetooth adapters. Run a repair shop? See Redline for shops.
Generic OBD-II reference. Manufacturer-specific behavior varies. Confirm with a scan tool and, for safety-related codes, a professional inspection. Cost ranges are reference ranges, not quotes.
Seeing P0307 on your car?
Every problem becomes a Case. Tell Redline what the car is doing: it shows what the evidence supports, what’s still missing, and what to check next, before you approve a repair.
“Inner pad ~1 mm. Outer pad 3 mm.”
Next: check the slide pins move freely before buying parts.