P0306high severityDo not driveP0306 Code: Cylinder 6 Misfire Detected
Written in plain English and reviewed by the eli5cars editorial team · Last reviewed June 2026
What it means in plain English
P0306 tells you that cylinder number 6 in your engine is misfiring — meaning it's failing to ignite the air-fuel mixture on some or all of its firing strokes. Cylinder 6 only exists on engines with 6 or more cylinders, so this code appears on V6 and V8 (and larger) engines. On a V6, that's one-third of your cylinders failing to contribute; you'll feel rough running, shaking, and sluggishness. The ECM detected the problem by monitoring the crankshaft speed — a dead cylinder causes a tiny hesitation in rotation that the ECM catches.
⛔ Do not drive with this code active
This fault can cause immediate mechanical or safety damage. Have the vehicle towed or inspected before driving.
Most likely causes — ranked
#1 Worn or fouled spark plug in cylinder 6
most likelyFix: Start by removing and inspecting the cylinder 6 spark plug. V6 and V8 engines often have rear bank plugs that are harder to reach — on some models this alone justifies a shop visit. A worn electrode gap, heavy carbon deposits, or an oil-soaked plug all cause misfires. Replace the full set if the engine is past 60,000 miles.
#2 Failed ignition coil on cylinder 6
likelyFix: Swap the cylinder 6 coil-on-plug (COP) with a coil from another cylinder. Clear the code and do a short test drive. If the misfire moves to the new cylinder (e.g., you now get P0304 instead of P0306), the coil is the problem. Replace the failed coil. On V6 engines, cylinder 6 is often on the rear bank — harder to access but still a DIY job with patience.
#3 Clogged or leaking fuel injector on cylinder 6
likelyFix: If the coil and plug are confirmed good, the fuel injector is next. A clogged injector delivers too little fuel (lean misfire); a stuck-open injector over-fuels (rich misfire). Try a fuel system cleaner additive as a low-cost first step. For confirmation, an injector balance or flow test at a shop pinpoints a bad injector. Replacement requires removing the fuel rail on that bank.
#4 Low compression in cylinder 6 (internal engine wear)
possibleFix: If all ignition and fuel components test fine, perform a compression test on cylinder 6. Low compression compared to adjacent cylinders indicates internal mechanical failure — worn piston rings, a damaged valve, or a head gasket breach. A leakdown test identifies where the compression is escaping. Repair costs escalate significantly at this stage.
Check engine light on? Get a free code scan
If your check engine light is on, most auto-parts stores (AutoZone, O'Reilly, Advance) will read the code for FREE — no purchase required, just walk in. Bring the code back here and look it up at eli5cars.com/obd2 for the plain-English explanation.
Note: a scan only helps when there's an active fault code. For purely mechanical symptoms (noises, vibrations, leaks), a scan may show nothing — the suspects listed above are your starting point.
Want to read the codes yourself?
First, the free option: AutoZone, O’Reilly, and Advance Auto Parts read your codes for free — no purchase needed. That’s the cheapest way to get the code to look up here. If you’d rather have your own so you can check anytime (and clear a code after a fix), the Veepeak OBDCheck BLE is an inexpensive, reliable plug-in reader that pairs with a free phone app and works on any car sold since 1996.
See the Veepeak OBD2 scanner on AmazonAffiliate link — we may earn a commission at no extra cost to you. Details.
Frequently asked questions
Can I drive with P0306?
Not safely for regular use. A misfiring cylinder 6 dumps raw fuel into the exhaust, which can destroy the catalytic converter on that bank within days of regular driving. Get the car to a shop or parts store for diagnosis. AutoZone and O'Reilly will read the code for free.
P0306 is common on which vehicles?
Any vehicle with 6 or more cylinders can set P0306 — it's common on Ford F-150 V6/V8, Chevrolet Silverado, Toyota Tacoma V6, Honda Pilot, and many others. On some Ford trucks the rear bank spark plugs are notoriously hard to reach; allow extra time for the DIY job.
Will ignoring P0306 damage my catalytic converter?
Yes. Raw fuel entering the exhaust ignites inside the catalytic converter instead, causing it to overheat and melt the internal honeycomb substrate. A P0420 or P0430 code appearing after a period of misfiring is the typical sign of cat damage. Fixing the misfire quickly protects the cat.
P0306 appeared alongside P0300 — what does P0300 mean?
P0300 is a random/multiple cylinder misfire code. The ECM sets it when the total misfire rate across all cylinders exceeds a threshold. P0306 tells you cylinder 6 is the source. Resolve the cylinder 6 issue and both codes should clear after a complete drive cycle.