P0306 on a Subaru: 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 Subaru

On a Subaru, P0306 means the engine computer detected that cylinder 6 is misfiring, so that cylinder is not producing power on schedule. Subaru is best known for four-cylinder boxer engines, so P0306 only appears on the six-cylinder models like the Tribeca and the 3.6R Outback and Legacy. A flashing light means the misfire is severe enough to risk catalytic converter damage.

Is P0306 common on Subarus?

P0306 is uncommon on Subaru because most models are four-cylinders. It shows up on the six-cylinder flat engines in the Tribeca and 3.6R Outback and Legacy, usually from worn spark plugs or failing coil-on-plug ignition coils. Fuel injector issues and low compression are less common causes.

Commonly reported on: Outback, Legacy, Tribeca.

Symptoms

Check engine light on (flashing if severe)
Rough idle or shaking while idling
Loss of power or hesitation under load
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	$80–300
Replace or clean the cylinder 6 fuel injector	Mechanic	$150–400
Run a compression test to rule out internal engine wear	Mechanic	$100–200