P0304 on Hyundai

Owners of the 1.6L Gamma GDI Accent report the engine burning a quart of oil in as little as 1,000 miles in the most severe reports, with many reporting 1-2 quarts between normal oil-change intervals. The cause is a combination of worn/coked piston rings and valve stem seals letting oil into the combustion chamber, plus a PCV system that pulls oil vapor into the intake. Because the injectors spray directly into the cylinder, there is no fuel washing the back of the intake valves, so the oil vapor bakes into hard carbon deposits that hurt sealing, idle quality and cold-start performance. Left unchecked, low oil level is also the fastest route to the rod-bearing failure the same engine is known for.

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.

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.

Certain 2019-2020 Elantra sedans built with the 2.0L Nu MPI (Atkinson-cycle) engine were assembled with piston oil rings whose nitride heat treatment was inconsistent, leaving the rings excessively hard. The hardened outer periphery of the oil ring chips, and the chipped material scuffs the cylinder bore. The failure progresses in a recognizable order: first rising oil consumption between changes, then a deep metallic knock under load, then bearing damage and finally seizure and stall in traffic. Because the oil ring is the control ring, owners often see oil level fall a quart or more per 1,000 miles well before any noise appears. This is a manufacturing/heat-treat defect confined to specific engine build ranges on the 2.0L Nu MPI - it is not the same failure as the Nu connecting-rod bearing knock, and it does not apply to the 1.6L Gamma T-GDI Sport or the 1.8L Nu.

The Elantra Sport's 1.6L Gamma T-GDI is a direct-injection-only engine: no fuel ever washes across the back of the intake valves, so oil vapour drawn in through the PCV system bakes onto the valve stems and seats. Owners on the Elantra Sport community report visible deposits by roughly 60,000-90,000 miles, and heavier deposits on cars driven mostly short-trip. The deposits disrupt airflow and swirl, producing a shaky cold idle, hesitation off boost, cylinder-specific misfires and a slow erosion of power and fuel economy that owners often mistake for normal ageing. Turbocharging worsens it because higher blow-by loads the PCV system with more oil mist. This is specific to the direct-injected 1.6T - the port-injected 1.8L and 2.0L Nu MPI engines sold in the same bodies wash their intake valves with fuel and do not accumulate deposits this way.

On the 2.5L Smartstream GDI+MPI engine (G4KR) used in the TM Santa Fe from 2021, the internal filter/screen inside the direct injector can break apart and the injector leaks fuel into the cylinder after shutdown and at idle. Owners report a hard hot start, raw-fuel smell, rough idle, single- or multi-cylinder misfires, loss of power and stalling while driving; the leaking fuel also dilutes the engine oil. Hyundai addressed it with TSB 23-FL-002H-1, which lists the diagnosis and replacement procedure for internally leaking GDI injectors and was later expanded to a wider production date range covering Santa Fe, Tucson and Santa Cruz. A 2025 class action alleges Hyundai has still not recalled the vehicles. Note the earlier 2.4L Theta II GDI injectors are a different part and this pattern is specific to the 2.5L.

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.

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.

Both the naturally aspirated 1.6 Gamma GDI (G4FD) and the 1.6 Gamma T-GDI (G4FJ) in the first-generation Veloster inject fuel directly into the cylinder, so nothing washes the intake valves. PCV oil vapor bakes onto the valve backs and, by roughly 60,000-100,000 miles, deposits restrict airflow and prevent proper seating. Owners report rough cold idle, intermittent single-cylinder misfire codes (P0301-P0304), hesitation and a gradual loss of power; several owner photo logs on the Veloster forums track the deposit growth. Dealers frequently replace plugs or coils first because the codes look like ignition faults.