P0306 on a Mazda: Causes, Fixes & Repair Cost

🟠 Moderate severity · drivable

If the check engine light is flashing, stop driving — a severe misfire can damage the catalytic converter. A steady light is usually safe for a short drive to a shop.

What P0306 means on a Mazda

On a Mazda, P0306 means the engine computer detected that cylinder 6 is misfiring, so that cylinder is not producing power on schedule. Modern Mazdas are four-cylinders, so P0306 points to older V6 models like the CX-9 and the V6 Mazda6. A flashing light means the misfire is severe enough to risk catalytic converter damage.

Is P0306 common on Mazdas?

P0306 appears on Mazda V6 models like the first-generation CX-9 and the V6 Mazda6, most often at higher mileage. Worn spark plugs and failing ignition coils are the usual causes on the 3.0L and 3.7L V6 engines. Fuel injector issues and low compression are less common causes.

Commonly reported on: CX-9, Mazda6, Millenia.

Symptoms

Check engine light on (flashing if severe)
Rough idle or shaking while idling
Loss of power or hesitation when accelerating
Poor fuel economy

Common causes

most common: Failing ignition coil on cylinder 6
common: Worn or fouled spark plug in cylinder 6
common: Clogged or leaking fuel injector on cylinder 6
less common: Damaged wiring or connector at the cylinder 6 coil
rare: Low compression in cylinder 6 from engine wear

How to fix it

Fix	DIY?	Typical cost
Replace the ignition coil on cylinder 6	Yes	$80–350
Replace worn spark plugs	Yes	$60–250
Replace or clean the cylinder 6 fuel injector	Mechanic	$150–400
Run a compression test to rule out internal engine wear	Mechanic	$100–200