P0306: Cylinder 6 Misfire Detected
The engine computer has detected repeated misfires in cylinder 6.
What P0306 means
P0306 means cylinder 6 is not contributing its share of power. The engine computer sees the crankshaft slow down on the stroke when cylinder 6 should fire and counts how often it happens. Above a set rate, usually within a few hundred to a thousand revolutions, it sets the code. On a V6, cylinder 6 is the last cylinder on one bank; on a V8 it sits mid bank. Shops look for the simple causes first. A coil swap moves the ignition parts around; if the misfire follows, the coil is bad. If not, they check the plug for oil, carbon or a cracked insulator and test the injector. A vacuum leak near one runner or a stuck PCV valve can lean out a single cylinder too. Mechanical problems such as a burnt exhaust valve are less common but show up as low compression. Get it done soon, because repeated misfires overheat the catalytic converter on that bank.
Common symptoms
- Check engine light on, or flashing when the misfire is bad
- Rough or shaky idle
- Hesitation or jerking when you accelerate
- Loss of power, especially going uphill or merging
- Worse gas mileage
Most common causes
- Bad ignition coil or plug wire
- Worn or cracked spark plug
- Fuel injector problem on cylinder 6
- Vacuum leak at the PCV valve or intake near cylinder 6
- Valve cover gasket leak fouling the plug
- Mechanical issue such as a burnt valve
What to check yourself first
Find cylinder 6 on your engine diagram and check whether its coil is reachable. Inspect the PCV valve and nearby vacuum hoses for cracks. A coil swap that moves the code to another cylinder confirms a bad coil.
Typical fixes and what they cost
| Fix | Typical cost | Note |
|---|---|---|
| Replace ignition coil | $238-$320 | Confirm with a swap test before buying a coil. |
| Replace spark plugs | $288-$399 | A full set is best on a V6 so all cylinders match. |
| Replace fuel injector | $768-$953 | Replaced after it fails a balance or resistance test. |
| Replace PCV valve | $124-$173 | If the PCV valve or hose is leaking vacuum near that cylinder. |
| Check engine light diagnosis at a shop | $125-$183 | Adds compression and leak down testing when ignition and fuel are fine. |
Typical US price ranges for parts and labor, not quotes. Your shop should confirm the cause with a diagnostic before replacing parts.
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Related codes
- P0300 Random/Multiple Cylinder Misfire Detected
- P0305 Cylinder 5 Misfire Detected
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