P0304 on Genesis
Cylinder 4 Misfire Detected
P0304 on Genesis vehicles indicates cylinder 4 misfire detected. Au7o has documented this code across 2 Genesis models — most commonly on G70, GV80. 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 Genesis range from $400 to $900, 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 Genesis by Model
Genesis G70(1 issue)
- GDI Intake-Valve Carbon Buildup (Misfires, Rough Idle)2019-2024
Like most gasoline direct-injection engines without supplemental port injection, the G70's 2.0T and 3.3T accumulate carbon on the backs of the intake valves over time because no fuel washes them. Owners report heavy valve coking by ~24,000 miles in some cases, especially when combined with oil consumption. The deposits disrupt airflow and seating, causing rough idle, hesitation, cold-start stumble, and cylinder misfire codes. Removing the intake to walnut-blast the valves is the definitive fix.
Genesis GV80(1 issue)
- 2.5L T-GDI Cold-Start Misfire P0300-P0304 (Service Campaign 914G / TSB 25-01-051G)2021-2024
Theta III 2.5L T-GDI engines in GV80 JX1 (and related G80/GV70) illuminate the Check Engine light with random or specific cylinder misfire codes P0300-P0304 during cold start. Root cause is identified as ECM misfire-detection logic; Genesis issued service campaign 914G covering 2021-2024MY GV80 built 07/27/2020-03/04/2024 for a free ECM reflash.
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View P0304 across all makes →Frequently Asked Questions
What does P0304 mean on Genesis?▼
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 Genesis specifically, this code is documented across 2 models.
What causes P0304 on Genesis vehicles?▼
Common causes on Genesis: 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 Genesis?▼
Repair costs on Genesis range from $400 to $900, depending on the specific model and root cause.
Which Genesis models have P0304 documented?▼
Au7o has documented P0304 on 2 Genesis models: G70, GV80.