The Mercedes-Benz M 257.920 is a 2,999 cc, inline-six, turbocharged petrol engine produced between 2017 and present. It features a 30° canted inline-six configuration with twin-scroll turbocharging, 48-volt EQ Boost mild hybrid system, and direct fuel injection at up to 350 bar, delivering 270 kW (367 PS) in standard tuning, with peak torque of 500 Nm available from 1,800 to 5,800 rpm.
Fitted to mid-size and full-size luxury sedans and SUVs such as the W222 S-Class, W213 E-Class, and W167 GLE, the M 257.920 was engineered for smooth power delivery, improved efficiency, and reduced emissions. Emissions compliance was achieved through exhaust gas recirculation (EGR), close-coupled three-way catalysts, and secondary air injection, enabling Euro 6d-TEMP compliance across all markets.
One documented engineering update occurred in 2020, when Mercedes-Benz revised the turbocharger compressor housing and ECU mapping to improve transient response and thermal management. This update, referenced in Mercedes-Benz Technical Bulletin 07.0250/20, also included recalibrated EQ Boost integration and modified ignition timing to support improved cold-start performance and reduced particulate emissions.
All production units (2017–present) meet Euro 6d-TEMP emissions standards (VCA UK Type Approval #VCA/EMS/9013). No non-compliant variant was produced.
The Mercedes-Benz M 257.920 is a 2,999 cc inline-six engineered for premium sedans and SUVs (2017–present). It combines a DOHC 24-valve layout with twin-scroll turbocharging and 48-volt EQ Boost system to deliver refined, responsive performance. Designed to meet Euro 6d-TEMP standards, it balances electrified efficiency with strong torque delivery.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 2,999 cc | |
| Fuel type | Petrol | |
| Configuration | Inline-6, DOHC, 24-valve | |
| Aspiration | Turbocharged | |
| Bore × stroke | 83.0 mm × 92.0 mm | |
| Power output | 270 kW (367 PS) @ 5,250–6,100 rpm | |
| Torque | 500 Nm @ 1,800–5,800 rpm | |
| Fuel system | High-pressure direct injection (up to 350 bar) | |
| Emissions standard | Euro 6d-TEMP | |
| Compression ratio | 10.5:1 | |
| Cooling system | Water-cooled | |
| Turbocharger | Single twin-scroll turbo (BorgWarner) | |
| Timing system | Double roller chain (primary and secondary) | |
| Oil type | 0W-40 (MB 229.52) | |
| Dry weight | 184 kg |
The turbocharged inline-six provides seamless power delivery ideal for luxury driving but requires consistent use of 0W-40 MB 229.52 oil to maintain turbocharger and timing chain longevity. Oil changes every 15,000 km or annually are recommended, especially in mixed driving conditions. The EQ Boost system demands stable 48-volt electrical supply; degraded belt alternator starter (BAS) or battery can cause limp mode. Engines built before 2020 should be verified for turbocharger and ECU upgrades per Technical Bulletin 07.0250/20 to ensure transient response and thermal stability. Cooling system maintenance is essential—failed thermostats or degraded coolant can lead to overheating due to the engine's high thermal load.
Oil Specs: Requires MB 229.52 specification (0W-40) (Mercedes-Benz SIB 07.0250/20). Compatible with ACEA A3/B4 standards.
Emissions: Certified to Euro 6d-TEMP only (VCA Type Approval #VCA/EMS/9013). No production units meet Euro 7 standards.
Power Ratings: Measured under DIN 70020 standards. Output consistent across all markets; no fuel quality dependency above RON 95.
Mercedes-Benz Technical Information System (TIS): Docs A32500, A32510, SIB 07.0250/20
VCA Type Approval Database (VCA/EMS/9013)
DIN 70020 Engine Power Testing Standard
The Mercedes-Benz M 257.920 was used across Mercedes-Benz's W222/W213/W167 platforms with longitudinal mounting and no external licensing. This engine received platform-specific adaptations-reinforced engine mounts in the W222 and revised exhaust manifolds in the W167-and from 2023 the W223 S-Class adopted the M 256-based M 256H hybrid variant, creating interchange limits. All adaptations are documented in OEM technical bulletins.
Locate the engine code stamped diagonally on the front right cylinder block near the alternator (Mercedes-Benz TIS A32500). The 7th VIN digit indicates engine type ('P' for M 257 series). Pre-2020 models have silver valve covers with ribbed finish; post-2020 units use black valve covers with updated turbocharger housing. Critical differentiation from M 274: M 257.920 uses 48-volt EQ Boost and twin-scroll turbo; M 274 uses conventional starter and single-scroll turbo. Service parts require production date verification—turbochargers and ECUs for pre-2020 engines are incompatible with later units due to hardware and calibration changes (Mercedes-Benz SIB 07.0250/20).
The M 257.920's primary reliability risk is 48-volt EQ Boost system failure in early builds, with elevated incidence in high-mileage or poorly maintained vehicles. Internal Mercedes service reports from 2019 indicated a notable number of pre-2020 engines required BAS replacement before 120,000 km, while UK DVSA data shows electrified engines are overrepresented in MOT emissions failures due to aging oxygen sensors and exhaust leaks. Extended oil intervals and infrequent driving exacerbate electrical system stress, making oil quality and regular maintenance critical.
Analysis derived from Mercedes-Benz technical bulletins (2017–2025) and UK DVSA failure statistics (2018–2024). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about MERCEDES-BENZ M257920.
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