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…
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 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.
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.
The most common questions about engine codes, what they mean, how to find them and how this database works
The M 257.920 delivers smooth, responsive performance but early models (2017–2019) are prone to EQ Boost (BAS) and turbocharger issues. Later units (post-2020) with revised components are more durable. Longevity depends heavily on maintenance—consistent oil changes with 0W-40 MB 229.52 oil and attention to hybrid and cooling systems are essential for reliable operation beyond 120,000 km.
Key issues include EQ Boost (BAS) failure, turbocharger bearing wear, ignition coil failures, and cooling system leaks. These are documented in Mercedes-Benz service bulletins. Regular inspection of BAS, turbocharger, and cooling components can prevent major failures and maintain peak performance.
The M 257.920 was used in the W222 S-Class (S 450, 2017–2020), W213 E-Class (E 450, 2017–2023), and W167 GLE-Class (GLE 450, 2018–2023). It was the first inline-six to feature EQ Boost mild hybrid technology. No external licensing or cross-manufacturer applications are documented.
Yes, within limits. ECU remapping can achieve gains of ~20-40 kW due to the engine's robust internals. Performance is best enhanced through exhaust, intake, and intercooler upgrades while preserving reliability. Over-tuning risks damaging the turbocharger and EQ Boost system due to the engine's integrated electrification and thermal loads.
Fuel consumption is moderate for a turbocharged six-cylinder. In the E 450 (W213), typical usage is ~9.8 L/100km (city) and ~7.2 L/100km (highway), or approximately 34 mpg UK combined. Real-world figures vary with driving style, but expect 30–36 mpg (UK) in mixed conditions. The EQ Boost system contributes to improved efficiency in urban driving.
Yes. The M 257.920 is an interference engine. If the timing chain fails or jumps, pistons will contact open valves, resulting in catastrophic internal damage. While the double roller chain design is robust, regular inspection and adherence to maintenance schedules are critical to prevent failure.
Mercedes-Benz specifies 0W-40 oil meeting MB 229.52 standard. Use only high-quality synthetic oils designed for turbocharged petrol engines. Change oil every 15,000 km or annually to ensure proper turbocharger and timing chain lubrication, preventing premature wear under aggressive driving conditions.
Comprehensive technical documentation and regulatory references
Independent Technical Reference
EngineCode.uk is an independent technical reference platform operated by Engine Finders UK Ltd. We are not affiliated with MERCEDES-BENZ or any other manufacturer. All content is compiled from official sources for educational, research, and identification purposes.
Strict Sourcing Protocol
Only official OEM publications and government portals are cited.
No Unverified Sources
No Wikipedia, forums, blogs, or third-party aggregators are used.
Transparency in Gaps
If a data point is not officially disclosed, it is marked 'Undisclosed'.
Regulatory Stability
EU regulations are referenced using CELEX identifiers for long-term stability.
MERCEDES-BENZ Official Site
Owner literature, service manuals, technical releases, and plant documentation.
EUR-Lex
EU emissions and type-approval regulations (e.g., CELEX:32007R0715, CELEX:32017R1151).
GOV.UK: Vehicle Approval & V5C
UK vehicle approval processes, import rules, and MoT guidance.
DVLA: Engine Changes & MoT
Official guidance on engine swaps and inspection implications.
Vehicle Certification Agency (VCA)
UK type-approval authority for automotive products.
Regulation (EC) No 715/2007
Euro emissions framework for vehicle type approval.
Commission Regulation (EU) 2017/1151
WLTP and RDE testing procedures for emissions certification.
GOV.UK: Vehicle Approval
UK compliance and certification requirements for imported and modified vehicles.
VCA Certification Portal
Type-approval guidance and documentation.
Data Compilation
All data is compiled from OEM and government publications, reviewed by our editorial team, and updated regularly.
Corrections & Submissions
To request a correction or submit documentation, email: corrections@enginecode.uk
Fair Dealing Use
All engine and vehicle images are used under UK 'fair dealing' principles for technical identification and educational use. Rights remain with their respective owners.
Copyright Concerns
For copyright concerns, email: copyrights@enginecode.uk
GDPR Compliance
EngineCode.uk complies with UK GDPR. We do not collect personal data unless explicitly provided.
Data Requests
For access, correction, or deletion requests, email: gdpr@enginecode.uk
Trademark Notice
All trademarks, logos, and engine codes are the property of their respective owners. Use on this site is strictly for reference and identification.
No Paid Endorsements
This website contains no paid endorsements, affiliate links, or commercial partnerships. We do not sell parts or services.
Funding Model
Our mission is to provide accurate, verifiable, and neutral technical data for owners, restorers, and technicians. This site is self-funded.
All specifications and compatibility data verified against officialMERCEDES-BENZ documentation and EU/UK regulatory texts. Where official data is unavailable, entries are marked “Undisclosed”.
All external links open in new tabs. Please verify current availability of resources.