What are the most common causes of P0306?

The most common causes are: Bad ignition coil on cylinder 6; Worn or fouled cylinder 6 spark plug; Clogged or leaking cylinder 6 fuel injector; Intake plenum or vacuum leak on that bank; Low compression in cylinder 6.

How much does it cost to fix P0306?

Typical US independent-shop repair cost for P0306 runs about $100 - $600, depending on the root cause. Common fixes: Replace the cylinder 6 ignition coil (about $100 - $350 at a shop); Replace the spark plugs (rear-bank access) (about $150 - $500 at a shop); Replace the cylinder 6 fuel injector (about $150 - $600 at a shop).

Will P0306 clear itself?

No, not on its own. P0306 will keep coming back every time the relevant monitor re-runs until the underlying cause is actually repaired - clearing it with a scan tool without fixing what triggered it only delays the light coming back on.

P0306: Cylinder 6 Misfire Detected

P0306 quick answer

P0306 means cylinder 6 is misfiring. It is usually the cylinder 6 coil or spark plug; on many V6 engines that cylinder is on the rear bank, so labor is the main cost.

Severity: Moderate
Can I drive? Short-term, usually yes, if the check-engine light is steady. Plan the repair soon, since each misfire sends unburned fuel toward the catalytic converter.
Typical fix: $100 - $600

Also written as PO306 or P306 or P 0306.

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What P0306 means

P0306 means the engine computer detected a misfire in cylinder 6. It only appears on six- and eight-cylinder engines, and on many transverse V6 engines cylinder 6 sits on the rear bank against the firewall, under the intake plenum. The cause is usually the coil, plug, or injector for that cylinder; access, not diagnosis, is what makes it harder than a front-bank misfire.

Symptoms of P0306

Rough idle and vibration
Stumble under acceleration
Flashing check-engine light during a hard misfire
Loss of power and fuel economy

Is it safe to drive with P0306?

Short-term, usually yes, if the check-engine light is steady. Plan the repair soon, since each misfire sends unburned fuel toward the catalytic converter. If the light flashes, stop driving hard - a flashing light means the misfire is severe enough to overheat the converter.

What the P0306 fix costs

Fix	DIY parts	At a shop
Replace the cylinder 6 ignition coil	$25 - $100	$100 - $350
Replace the spark plugs (rear-bank access)	$25 - $90	$150 - $500
Replace the cylinder 6 fuel injector	$40 - $150	$150 - $600

Ranges are rounded and for the US market only - actual price depends on region, shop labor rates, and the exact make and model.

Parts that commonly fix P0306

Ignition coil - Cause #1 for a single-cylinder misfire - prove it with the coil swap test first
Spark plugs - Cause #2: worn or fouled plugs. Replace as a set, in the heat range your engine specifies
Inline spark tester - Shows whether the coil is delivering spark to that cylinder in seconds
Dielectric grease - A thin coat inside the coil boot stops the arcing and moisture that cause repeat misfires
Compression tester - For when the misfire stays put after coil and plug swaps - rules low compression in or out
OBD-II scanner - Reads and clears codes, and shows live data so you fix the cause rather than the symptom

Most of these open an Amazon search - add your year, make and model, because most of these parts are fitment-specific. A few link straight to the exact tool or part we have verified, because it fits any vehicle.

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What P0306 actually means

P0306 means the engine computer detected repeated misfires in cylinder 6. Because it takes six cylinders to have a cylinder 6, this code only shows up on V6, inline-six, and V8 engines - and on many transverse V6 engines cylinder 6 lives on the rear bank, tucked against the firewall under the intake plenum. That location is the whole story of P0306: the diagnosis is the usual coil, plug, and injector routine, but getting to the parts is what drives the time and the cost.

How to diagnose P0306 step by step

Step 1: Confirm which bank cylinder 6 is on Look up the cylinder numbering for your engine. On many front-wheel-drive V6s the even cylinders are on the rear bank, against the firewall; on others the numbering runs down one bank first. Knowing whether you face an easy front-bank job or a plenum-removal job decides whether you test in the driveway or book a shop.
Step 2: Check freeze-frame and misfire counts Record the RPM, load, and temperature when P0306 set, and watch per-cylinder misfire counters if your scanner offers them. If cylinders 2 and 4 on the same bank also show counts, look for something shared by that bank - a vacuum leak or intake gasket - rather than a single coil.
Step 3: Swap the cylinder 6 coil to another cylinder If access allows, move the cylinder 6 coil to another cylinder on the same bank, clear the code, and drive. A misfire that follows the coil condemns it. If the rear-bank coil needs the plenum off to reach, test for spark with an inline tester first so you only open things up once.
Step 4: Inspect the cylinder 6 plug and boot Rear-bank plugs are often the most neglected because they are hard to reach. Look for carbon tracking on the insulator or inside the coil boot, oil in the plug well, or a worn-wide gap. Carbon tracking or oil means replace the plug and boot and fix the leak; a clean plug points you onward to fuel and compression.
Step 5: Listen to and swap the cylinder 6 injector An injector that is not clicking at idle, or one that moves the misfire when swapped with a neighbor, is the culprit. Rear-bank injectors usually share the plenum removal with the coils, so if you are already opened up, this is the time to check it rather than closing up and guessing.
Step 6: Compression-test cylinder 6 last If spark and fuel are both good, compare cylinder 6 compression with the others. A reading well below the rest means a valve or ring problem inside the cylinder. At that point parts on the outside of the engine will not help, and a leak-down test tells you which it is.

The most common P0306 misdiagnosis

The costly P0306 mistake is replacing only the cylinder 6 coil on a rear-bank engine, closing everything up, and then pulling the plenum again months later for the plugs. When access is the expensive part, do the whole rear bank of plugs in one visit.

Tools you need for P0306

Inline spark tester - Checks rear-bank spark before you commit to removing the intake plenum.
OBD2 scanner with misfire counts - Shows whether the misfire is cylinder 6 alone or spread across one bank.
Compression tester - Rules out a mechanical cause in cylinder 6 before you spend more on ignition parts.

Parts you may need for P0306

Ignition coil - The usual cylinder 6 fix. Rear-bank coils run hotter against the firewall and fail more often on some engines.
Spark plugs (full set) - If the plenum is coming off anyway, doing all six plugs at once saves paying that labor twice.
Intake plenum gasket set - Needed if you remove the upper intake to reach rear-bank coils and plugs - do not reuse old gaskets.

P0306: DIY or pay a shop?

Difficulty: Moderate. Time: 1 - 3 hours. DIY parts: $25 - $200. Shop total: $120 - $500.

On an engine where cylinder 6 is on the front bank this is an easy DIY. On a transverse V6 where it sits under the plenum, it is still very doable at home with basic hand tools and new gaskets, but it is the job where most of the shop bill is labor - so replace all the rear plugs while you are in there.

How to stop P0306 coming back

Replace all spark plugs on schedule, including the rear bank. Rear-bank plugs are the ones that get skipped because they are hard to reach, and a worn plug strains its coil until it fails. Keeping all six on the same schedule is what keeps cylinder 6 from being the weak link. ServiceSage tracks the spark plug interval for your exact vehicle and reminds you before it is due, so the hard-to-reach cylinders get done with the rest. Track this maintenance free.