P0304 on Buick
Cylinder 4 Misfire Detected
P0304 on Buick vehicles indicates cylinder 4 misfire detected. Au7o has documented this code across 2 Buick models — most commonly on Lucerne, Regal. This code means the engine computer detected a misfire in cylinder number 4 — that cylinder isn't igniting its air-fuel mixture fully or at all. The system detects this by monitoring small changes in crankshaft rotation speed as each cylinder fires. You may feel a rough idle, shaking, hesitation or reduced power, and a persistent misfire can dump unburned fuel into the exhaust and overheat or damage the catalytic converter. Since it's pinpointed to one cylinder, the problem typically lies in that cylinder's spark, fuel, or compression. Typical repair costs on Buick range from $400 to $7,500, depending on the specific model and root cause.
Common Causes of P0304
- •Worn or fouled spark plug in cylinder 4
- •Failed or weak ignition coil on cylinder 4
- •Faulty spark plug wire or boot (where applicable)
- •Clogged, stuck or leaking fuel injector for cylinder 4
- •Vacuum or intake air leak near that cylinder
- •Low compression (worn rings, burnt/leaking valve, head gasket)
- •Damaged wiring or connector at the coil or injector
P0304 on Buick by Model
Buick Lucerne(1 issue)
- Lucerne Northstar V8 Head Bolt Pull / Coolant Loss2006-2011
The 4.6L Northstar V8 in 2006-2011 Lucerne CXS/Super (and STS, DTS, Cadillac SLS) is known for head-bolt thread pull from the aluminum block. Bolts back out of the block (rather than head gasket failing outright), allowing combustion gases into the coolant. Symptoms: coolant loss, white smoke, overheating, eventually no-start.
Buick Regal(1 issue)
- Carbon Buildup on Intake Valves (Direct Injection)2011-2017
Like other GM direct-injected engines, the Regal's 2.0T and 2.4L DI engines accumulate carbon deposits on the back of the intake valves because fuel no longer washes the valves clean. Over tens of thousands of miles this causes cold-start misfires, rough idle, hesitation, and reduced power and economy. It is a well-documented owner complaint on the turbo cars in particular.
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View P0304 across all makes →Frequently Asked Questions
What does P0304 mean on Buick?▼
P0304 stands for "Cylinder 4 Misfire Detected." This code means the engine computer detected a misfire in cylinder number 4 — that cylinder isn't igniting its air-fuel mixture fully or at all. The system detects this by monitoring small changes in crankshaft rotation speed as each cylinder fires. You may feel a rough idle, shaking, hesitation or reduced power, and a persistent misfire can dump unburned fuel into the exhaust and overheat or damage the catalytic converter. Since it's pinpointed to one cylinder, the problem typically lies in that cylinder's spark, fuel, or compression. On Buick specifically, this code is documented across 2 models.
What causes P0304 on Buick vehicles?▼
Common causes on Buick: Worn or fouled spark plug in cylinder 4, Failed or weak ignition coil on cylinder 4, Faulty spark plug wire or boot (where applicable), Clogged, stuck or leaking fuel injector for cylinder 4, Vacuum or intake air leak near that cylinder. Specific causes vary by model and year — see the per-model sections below.
How much does it cost to fix P0304 on a Buick?▼
Repair costs on Buick range from $400 to $7,500, depending on the specific model and root cause.
Which Buick models have P0304 documented?▼
Au7o has documented P0304 on 2 Buick models: Lucerne, Regal.