OBD codes / P0306
P0306
SeriousCylinder 6 Misfire Detected
Treat P0306 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. P0306 points to one specific cylinder — number 6 — 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 P0306 for my exact vehicle →
How to fix P0306
Moderate — doable at home with common tools and patience
- Pin down cylinder 6's location
Cylinder 6 appears only on six-cylinder-and-up engines, and on transverse V6s it's frequently on the hard-to-reach rear bank. Pull up a cylinder-numbering diagram for your exact engine and plan the job around access.
- Swap the number 6 coil with a front-bank coil
Exchange coil 6 with an accessible known-good coil, clear codes, and drive it. If a misfire code pops up on the coil's new cylinder, coil 6 was the culprit; if P0306 returns, move down the list.
- Change the cylinder 6 spark plug
Inspect plug 6 for oil fouling, carbon, or electrode wear while the coil is out. Given the effort of reaching this cylinder on many engines, replacing all the plugs on that bank at the same time is usually the smart move.
- Confirm injector 6 works
Check injector 6 for a steady click at idle or measure its coil resistance and compare it with its neighbors. An injector that's silent or reads open explains a fuel-side misfire on that cylinder.
- Test compression before any big spend
If ignition and fuel both pass, compression-test cylinder 6 and compare it to the rest. A low hole means internal engine work — get a professional leak-down diagnosis before authorizing anything expensive.
DIY or shop? On an inline six or a longitudinal V6 with room to work, this is normal DIY territory. On a transverse V6 where cylinder 6 hides behind the intake against the firewall, the coil swap alone may require plenum removal — that's shop work for most people, both for the specialty gaskets and the risk of a vacuum leak if reassembly isn't right.
Tools for the DIY steps: OBD-II scanner · Spark plug socket and swivel · Long extensions and universal joint · Multimeter · Torque wrench
Not sure which step applies to your car? Get the likely cause for your exact vehicle before buying anything for P0306.
P0306 on specific vehicles
The likely causes shift by model. We’ve written up the patterns we see most:
Frequently asked
Can I drive with P0306?
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 6'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 P0306?
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 6?
If only cylinder 6 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 P0306.
Seeing P0306 on your car? Get a diagnosis specific to your exact year, make and model.
Diagnose P0306 for my vehicleRelated trouble codes
Don’t have a scanner yet? A ~$25 Bluetooth adapter reads codes like P0306 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.