P0304 on Hyundai
Cylinder 4 Misfire Detected
P0304 on Hyundai vehicles indicates cylinder 4 misfire detected. Au7o has documented this code across 4 Hyundai models — most commonly on Elantra, Santa Fe, Sonata. 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 Hyundai range from $120 to $8,000, 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 Hyundai by Model
Hyundai Elantra(2 issues)
- Nu Engine Bearing Failure and Seizure2011-2016
The 1.8L Nu engine in 2011-2016 Elantras is prone to premature failure due to manufacturing defects including piston ring issues, connecting rod bearing failure, and oil passage problems. Metal debris from failed components can circulate through the engine causing catastrophic damage. A class action settlement covered these vehicles with extended warranty up to 140,000 miles.
- Valve Cover Gasket Oil Leaks Onto Spark Plug Wells and Exhaust Manifold2001-2006
The 2.0L Beta engine in this generation commonly develops valve cover gasket leaks as the rubber hardens with age and heat. Owners report oil seepage down the cylinder head, burning-oil smell, and in some cases oil collecting in spark plug wells that contributes to misfires. This is a well-known age-related issue in owner forums and repair databases for the XD Elantra.
Hyundai Santa Fe(1 issue)
- Excessive Oil Consumption - 2.4L GDI Engine2013-2019
The 2.4L GDI engine in Santa Fe models can consume excessive oil, sometimes 1 quart every 1,000-1,500 miles. This is related to carbon buildup on piston rings and intake valves inherent to GDI engines. Low oil can lead to engine damage if not monitored. Hyundai has an oil consumption test procedure for affected vehicles.
Hyundai Sonata(2 issues)
- Theta II Engine Seizure/Failure2011-2019
The Theta II engine can seize due to metal debris blocking oil flow to connecting rod bearings. Hyundai issued recalls and extended warranties. Affected engines may need replacement.
- Fuel Injector Failure Causing Misfire, Rough Running, and Check Engine Light2022-2025
Multiple owners of DN8-generation Sonata models report individual direct-injection fuel injectors failing, leading to cylinder-specific misfires, rough idle, hesitation, and flashing or steady MIL illumination. Reports are concentrated on the 2.5L Smartstream engine family and often involve one injector failing first, with some owners later replacing additional injectors. The issue is documented in owner complaints and forum discussions describing injector replacement as the corrective action.
Hyundai Tucson(1 issue)
- Theta II Engine Seizure Due to Connecting Rod Bearing Failure2011-2019
The Theta II GDI engine in 2011-2019 Tucson models is susceptible to connecting rod bearing failure caused by manufacturing debris restricting oil flow. This can lead to catastrophic engine seizure, often without warning. Hyundai issued multiple recalls (19V-601, 20V-150) and extended the engine warranty to 15 years/unlimited miles for original owners.
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View P0304 across all makes →Frequently Asked Questions
What does P0304 mean on Hyundai?▼
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 Hyundai specifically, this code is documented across 4 models.
What causes P0304 on Hyundai vehicles?▼
Common causes on Hyundai: 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 Hyundai?▼
Repair costs on Hyundai range from $120 to $8,000, depending on the specific model and root cause.
Which Hyundai models have P0304 documented?▼
Au7o has documented P0304 on 4 Hyundai models: Elantra, Santa Fe, Sonata, Tucson.