P0306 on a Jeep: 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 Jeep

On a Jeep, P0306 means the engine computer detected that cylinder 6 is misfiring, so that cylinder is not producing power on schedule. It appears on six-cylinder Jeeps like the Grand Cherokee, Wrangler, and Liberty, which use one ignition coil per cylinder. A flashing light means the misfire is severe enough to risk catalytic converter damage.

Is P0306 common on Jeeps?

P0306 shows up on six-cylinder Jeeps like the Grand Cherokee and Wrangler with the 3.6L Pentastar V6, and on older models with the 4.0L inline-six. Ignition coils and spark plugs are the usual wear items. Fuel injector issues and engine wear are less common causes on these engines.

Commonly reported on: Grand Cherokee, Wrangler, Liberty, Cherokee.

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	$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