OBD-II Code · Powertrain
P0306
Cylinder 6 Misfire Detected
Severity
high
Left alone, this one tends to take other parts with it.
Can you drive it
Depends on the light
Flashing: stop as soon as it is safe to — raw fuel is reaching the catalytic converter. Steady, and it only feels rough: a short drive to a shop is usually fine. Either way, stop if it shakes hard, loses power, overheats or makes a new noise.
Indicative cost (USD)
$30–$400
Varies by vehicle, diagnosis, parts, and local labor. This is not a repair quote.
Plug/coil first
Cylinder 6 misfire. V6/V8 only.
How a shop works this
The ECU has already told you which cylinder. That makes the fastest honest test a swap: move one part to another cylinder and see whether the fault moves with it. It identifies the fault instead of guessing at it, and it costs nothing.
Photograph the coils before you touch anything, and note which is which.
Cylinder numbering is not the same across manufacturers, and V6 and V8 bank layouts differ by maker — look up the firing order and bank layout for your engine before you move parts, or you can spend an hour swapping coils on the wrong bank.
Move the cylinder 6 ignition coil to a cylinder that is not misfiring, put that cylinder's coil on 6, clear the code, and run it until the misfire returns.
On a modern coil-on-plug engine the coil is the most common single answer to a cylinder-specific misfire, which is why it is the first thing to move — not because it is the cheapest part. A misfire that is there even at idle is the classic dead-coil pattern.
- The misfire follows the coil to its new cylinderThe coil is the fault. Replace it. If the engine has real mileage on it, the other coils are on the same clock.
- The misfire stays on cylinder 6The coil is fine. Look at the coil connector and the harness around it next — chafed and rodent-damaged connections at that plug are a common second answer — then pull the plug.
Read the plug you pulled, and check the boot for carbon tracking.
Black and sooty means it has been running rich. White or blistered means lean or too hot. Oil-wet points at valve seals or rings. Fuel-wet points at an injector holding open. A carbon-tracked boot arcs to the head and imitates a dead coil for the price of a new boot. On an older engine with a distributor, the cap, rotor and plug wires belong in this step too.
If spark is accounted for, go to fuelling, then to compression.
An injector balance or flow test comes first because it is quicker. Compression test second: a cylinder more than about 15% below its neighbours is mechanical, and no ignition part will fix it. A vacuum leak on this one runner sits alongside these — a leak big enough to affect every cylinder would be setting P0300 instead.
A flashing check-engine light means the misfire is putting raw fuel into the catalytic converter, which can destroy it quickly. Stop driving as soon as it is safe to. A steady light with a mild misfire is less urgent, but stop anyway if it shakes hard, loses power, overheats, or makes a noise it was not making before.
If the code comes back after a repair, the underlying fault is still there. That is the point to bring in a scanner with live data and freeze-frame, or a shop that has one.
Common symptoms
- Rough idle
- Check engine light
- Loss of power
Likely causes
- Failed ignition coil (cylinder 6)Most common
- Damaged coil connector or harness at cylinder 6
- Worn spark plug or carbon-tracked boot (cylinder 6)
- Clogged or leaking fuel injector (cylinder 6)
- Low compression on cylinder 6
- Vacuum leak at the cylinder 6 intake runner
Read the full diagnostic procedureP0306 means cylinder 6 is misfiring, which restricts you to engines with 6 or more cylinders.
P0306 means cylinder 6 is misfiring, which restricts you to engines with 6 or more cylinders.
Same diagnostic flow
- read the plug, swap the coil, swap the plug, compression test, injector balance.
- Cylinder 6 location depends entirely on engine architecture: on an inline-6 (BMW N52/N54/B58, Cummins, Toyota 2JZ), cylinder 6 is at the rear of the engine closest to the firewall and is historically the cylinder that runs hottest because the cooling system loses heat-rejection capacity by the time coolant reaches it.
- On a transverse V6 (Honda J35, Toyota 2GR-FE, Chrysler 3.6L), cylinder 6 is typically the rear-bank cylinder farthest from the accessory drive.
- On a Ford 5.4L 3V V8, cylinder 6 is on the left (driver's) bank, second from the front.
- Always confirm against the FSM before swapping parts.
Vehicle-specific patterns2006-2013 BMW N52/N54 inline-6 (328i, 335i, 528i) frequently throws P0306 from the well-known valve-cover gasket leak that drips oil into the spark-p…
- 2006-2013BMW N52/N54 inline-6 (328i, 335i, 528i) frequently throws P0306 from the well-known valve-cover gasket leak that drips oil into the spark-plug well of cylinder 6 specifically — cylinder 6 is the lowest point on the head and pools oil first.
- 2007-2012Nissan Pathfinder/Frontier with the VQ40DE 3.5L commonly throws P0306 from carbon-fouled intake valves and from a failed timing-chain tensioner that retards rear-bank cam timing.
- 2005-2010Mercedes-Benz M272/M273 V6/V8 frequently throws P0306 from the documented balance-shaft gear wear that retards cam timing — there's an extended warranty for affected VINs.
- 2004-2008Ford F-150 5.4L 3V throws P0306 from the same cam-phaser/stuck-plug issues as P0305.
Estimated repair$40 (single coil) to $4,500+ (balance-shaft job on the M272).
Look up another code
P0306 — frequently asked
What does a P0306 code mean?
Cylinder 6 misfire. V6/V8 only.
What causes a P0306 code?
Common causes: Failed ignition coil (cylinder 6); Damaged coil connector or harness at cylinder 6; Worn spark plug or carbon-tracked boot (cylinder 6); Clogged or leaking fuel injector (cylinder 6); Low compression on cylinder 6; Vacuum leak at the cylinder 6 intake runner.
What are the symptoms of a P0306 code?
Typical symptoms: Rough idle; Check engine light; Loss of power.
Is it safe to drive with a P0306 code?
Depends on the light. Flashing: stop as soon as it is safe to — raw fuel is reaching the catalytic converter. Steady, and it only feels rough: a short drive to a shop is usually fine. Either way, stop if it shakes hard, loses power, overheats or makes a new noise. Estimated repair: $30-$400 — plug/coil first.
How do I diagnose a P0306 code?
The ECU has already told you which cylinder. That makes the fastest honest test a swap: move one part to another cylinder and see whether the fault moves with it. It identifies the fault instead of guessing at it, and it costs nothing. 1. Photograph the coils before you touch anything, and note which is which. 2. Move the cylinder 6 ignition coil to a cylinder that is not misfiring, put that cylinder's coil on 6, clear the code, and run it until the misfire returns. 3. Read the plug you pulled, and check the boot for carbon tracking. 4. If spark is accounted for, go to fuelling, then to compression.
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