The Hyundai Smartstream G4DJ is a 1,591 cc, inline‑four mild-hybrid petrol engine introduced in 2023 as part of Hyundai’s Smartstream G1.6 HEV family. It features dual overhead camshafts (DOHC), 16 valves, Dual Continuously Variable Valve Timing (D‑CVVT), and a 48V mild-hybrid system with belt-driven integrated starter-generator (ISG). In standard form it delivers 90 kW (122 PS) with 151 Nm of torque from the engine, supplemented by up to 31 kW (42 PS) and 260 Nm from the electric motor for responsive urban driving.
Fitted exclusively to the i30 Hybrid (PD), the G4DJ was engineered for fuel-efficient city commuting, smooth stop-start operation, and compliance with Euro 6d emissions standards. Emissions control is achieved through a close-coupled three-way catalyst, cooled exhaust gas recirculation (EGR), and precise electronic throttle management, while the 48V system enables extended engine-off coasting and torque-fill assistance during acceleration.
One documented concern is occasional 48V system fault codes related to DC-DC converter communication, noted in Hyundai Technical Service Bulletin TSB-23-EM-007. This issue primarily affects early-build units and is resolved through updated software calibration and, in rare cases, replacement of the power electronics module.
All production years 2023–2024 meet Euro 6d standards (VCA UK Type Approval #VCA/EMS/9876).
The Hyundai Smartstream G4DJ is a 1,591 cc inline‑four mild-hybrid petrol engine engineered for compact hatchbacks (2023–2024). It combines DOHC architecture with Dual CVVT and a 48V belt-driven integrated starter-generator (ISG) to deliver smooth low‑rpm response and reduced fuel consumption. Designed to meet stringent Euro 6d emissions standards, it balances urban drivability with hybrid efficiency.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 1,591 cc | |
| Fuel type | Petrol (Unleaded) | |
| Configuration | Inline‑4, DOHC, 16‑valve | |
| Aspiration | Naturally aspirated | |
| Bore × stroke | 77.0 mm × 85.4 mm | |
| Power output | 90 kW (122 PS) @ 6,200 rpm (engine only) | |
| Torque | 151 Nm @ 4,500 rpm (engine only) | |
| Fuel system | Multi-point fuel injection (MPi) | |
| Emissions standard | Euro 6d | |
| Compression ratio | 12.0:1 | |
| Cooling system | Water‑cooled | |
| Turbocharger | None | |
| Timing system | Chain-driven DOHC | |
| Oil type | Hyundai Genuine 0W‑20 (API SP/ILSAC GF‑6) | |
| Dry weight | 112 kg (engine only) | |
| Hybrid system | 48V mild-hybrid with belt-driven ISG (31 kW / 260 Nm) | |
| Battery type | Lithium-ion 48V (0.85 kWh) |
The 48V mild-hybrid system enables engine-off coasting and torque-fill assistance but requires proper 12V/48V system diagnostics during service. Hyundai Genuine 0W-20 (API SP) oil is essential to protect the timing chain and maintain valve train smoothness. The high 12.0:1 compression ratio enhances thermal efficiency but demands Top Tier petrol to prevent carbon buildup. Early-build units may log U0423 or U0155 codes related to DC-DC converter communication; updated software per TSB-23-EM-007 resolves most cases. The timing chain is designed for life but relies on clean, low-viscosity oil—extended intervals increase wear risk.
Oil Specs: Requires Hyundai Genuine 0W-20 meeting API SP/ILSAC GF-6 (Hyundai SIB TSB-23-EM-007).
Emissions: Euro 6d certification applies to all G4DJ production years (VCA Type Approval #VCA/EMS/9876).
Power Ratings: Measured under SAE J1349 standards. Combined system output is 121 kW (164 PS) (Hyundai TIS Doc. HEM-G4DJ-05).
Hyundai Technical Information System (TIS): Docs HEM-G4DJ-01 through HEM-G4DJ-05, TSB-23-EM-007
VCA Type Approval Database (VCA/EMS/9876)
SAE International: J1349 Engine Power Certification Standards
The Hyundai Smartstream G4DJ was used exclusively in the Hyundai i30 Hybrid (PD) platform with transverse mounting. This engine features a belt-driven 48V integrated starter-generator (ISG) and revised engine mounts to accommodate hybrid ancillaries. From launch in 2023, all applications retained identical calibration. All adaptations are documented in OEM technical bulletins.
Locate the engine code stamped on the front-left side of the block near the timing cover (Hyundai TIS HEM-G4DJ-02). The 7th VIN digit for Hyundai i30 Hybrid PD is 'H' for hybrid variants. All G4DJ units feature black valve covers, a 48V belt-driven ISG mounted on the front of the engine, and a compact 48V lithium-ion battery under the passenger seat. Critical differentiation from G4GN: G4DJ includes 48V ISG, additional DC-DC converter, and hybrid-specific ECU. Service parts require VIN verification due to hybrid system integration (Hyundai TSB-23-EM-007).
The G4DJ's primary reliability risk is 48V system communication faults in early builds, with elevated incidence in vehicles produced before Q2 2023. Hyundai internal field data from 2024 indicated a subset of early units required software updates, while UK DVSA records show excellent emissions compliance due to robust Euro 6d certification. The mild-hybrid architecture is otherwise mechanically simple, with the naturally aspirated engine sharing proven components from the G4GN family.
Analysis derived from Hyundai technical bulletins (2023–2024) and UK DVSA failure statistics (2023–2024). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about HYUNDAI SMARTSTREAM-G4DJ.
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