P0304 on a Jeep: Causes, Fixes & Repair Cost

🟠 Moderate severity · drivable

A steady light usually means you can drive a short distance, but a flashing light means the misfire is severe — pull over and get the Jeep towed.

What P0304 means on a Jeep

On a Jeep, P0304 means the engine computer found that cylinder 4 is misfiring — it is not firing on schedule and contributing power. Because the code names a single cylinder, the problem is almost certainly that cylinder's own spark plug, ignition coil, or fuel injector. Modern Jeeps use coil-on-plug ignition, so each cylinder has its own coil and swapping coils is an easy test.

Is P0304 common on Jeeps?

P0304 shows up on Jeeps with coil-on-plug engines, most often the Wrangler and Grand Cherokee with the 3.6L Pentastar V6. Failing ignition coils and worn spark plugs are the usual causes as the miles add up. A clogged injector or an intake leak near cylinder 4 is less common.

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

Symptoms

Check engine light on, flashing if the misfire is severe
Rough idle or shaking while stopped
Loss of power or hesitation when accelerating
Worse fuel economy

Common causes

most common: Worn or fouled spark plug in cylinder 4
common: Failing ignition coil for cylinder 4
less common: Clogged or leaking fuel injector on cylinder 4
less common: Vacuum or intake air leak near cylinder 4

How to fix it

Fix	DIY?	Typical cost
Replace the spark plugs	Yes	$60–180
Replace the cylinder 4 ignition coil	Yes	$70–200
Swap the coil with another cylinder to confirm the fault first	Yes	$10–30
Replace the fuel injector on cylinder 4	Mechanic	$250–650