P0304 on a Lexus: 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 Lexus towed.

What P0304 means on a Lexus

On a Lexus, P0304 means the engine computer detected that cylinder 4 is misfiring — it is not burning fuel on schedule. Because the code names one cylinder, the fault is almost always that cylinder's own spark plug, ignition coil, or fuel injector. Lexus engines use coil-on-plug ignition, so swapping a coil between cylinders is an easy way to confirm the fault.

Is P0304 common on Lexuss?

P0304 shows up on Lexus models like the ES, RX, and IS, most often at higher mileage. Ignition coils on the V6 engines are a known wear item and fail with age, and spark plugs are due on long service intervals. A weak fuel injector is less common but possible on direct-injection engines.

Commonly reported on: ES, RX, IS, GX.

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: Low compression in cylinder 4 from engine wear

How to fix it

Fix	DIY?	Typical cost
Replace the spark plugs	Yes	$80–250
Replace the cylinder 4 ignition coil	Yes	$80–300
Swap the coil with another cylinder to confirm the fault first	Yes	$10–30
Replace the fuel injector on cylinder 4	Mechanic	$300–700