The Mercedes-Benz OM656.940 is a 2,925 cc, inline-six turbo-diesel engine produced between 2017 and 2023. It features common-rail direct injection, variable geometry turbocharging (VGT), and DOHC 24-valve configuration. In standard output, it delivers 230 kW (313 PS) and 700 Nm of torque, with applications across executive sedans and luxury SUVs.
Fitted to models such as the W213 E-Class, W222 S-Class, and W167 GLS-Class, the OM656.940 was engineered for smooth power delivery, refinement, and emissions compliance. Emissions compliance was achieved via exhaust gas recirculation (EGR), diesel particulate filter (DPF), and selective catalytic reduction (SCR) with AdBlue injection, enabling Euro 6 certification across its production run.
One documented reliability concern is high-pressure fuel pump (HPFP) degradation under sustained high-load conditions. This issue, highlighted in Mercedes-Benz Service Bulletin 20/2017, is linked to fuel contamination and marginal filtration in early builds. From 2019 onward, revised Bosch CP4-based fuel systems with improved filtration were implemented to enhance durability.
All production years (2017–2023) comply with Euro 6d-TEMP and Euro 6d standards depending on market and model year (VCA UK Type Approval #VCA/EMS/5688).
The Mercedes-Benz OM656.940 is a 2,925 cc inline-six turbo-diesel engineered for executive and luxury applications (2017–2023). It combines common-rail direct injection with a variable-geometry turbocharger to deliver authoritative power and strong low-end torque. Designed to meet Euro 6 emissions standards, it balances performance with efficiency and long-distance refinement.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 2,925 cc | |
| Fuel type | Diesel | |
| Configuration | Inline-6, DOHC, 24-valve | |
| Aspiration | Turbocharged | |
| Bore × stroke | 83.0 mm × 94.0 mm | |
| Power output | 230 kW (313 PS) @ 3,800 rpm | |
| Torque | 700 Nm @ 1,200–3,200 rpm | |
| Fuel system | Bosch CRS 3.0 common-rail (up to 1,800 bar) | |
| Emissions standard | Euro 6 (2017–2023) | |
| Compression ratio | 15.5:1 | |
| Cooling system | Water-cooled | |
| Turbocharger | Single variable-geometry turbo (Garrett GT2060V) | |
| Timing system | Dual chain (front-mounted, robust design) | |
| Oil type | MB 229.52 (SAE 0W-30) | |
| Dry weight | 198 kg |
The inline-six configuration provides smooth, linear power delivery ideal for highway cruising but demands strict adherence to 15,000 km oil change intervals using MB 229.52 specification oil to maintain turbo and HPFP longevity. Use of ultra-low-sulfur diesel (EN 590) is critical to prevent injector and fuel pump wear. Cold starts should be brief; prolonged idling increases EGR and DPF soot loading. Post-2019 models benefit from upgraded CP4 fuel pumps and enhanced filtration. EGR, DPF, and SCR systems require periodic regeneration and cleaning to prevent limp mode. Timing chains are generally durable but inspection is recommended beyond 200,000 km. AdBlue system maintenance is essential for Euro 6 compliance.
Oil Specs: Requires MB 229.52 specification (Mercedes-Benz SIB 22/2017). Not compatible with older MB 229.5 or ACEA A/B standards.
Emissions: Euro 6 certification applies to all 2017–2023 models (VCA Type Approval #VCA/EMS/5688). Compliance includes Euro 6d-TEMP and Euro 6d depending on model year.
Power Ratings: Measured under DIN 70020. Output maintained across EU and North American variants (Mercedes-Benz TIS Doc. M13520).
Mercedes-Benz Technical Information System (TIS): Docs M12690, M13152, SIB 20/2017, SIB 22/2017
VCA Type Approval Database (VCA/EMS/5688)
ISO 1585:1996 Road vehicles — Test code for net power of internal combustion engines
The Mercedes-Benz OM656.940 was used across Mercedes-Benz's W213/W222/W167 platforms with longitudinal mounting and no licensed external applications. This engine received platform-specific adaptations-reinforced engine mounts in the W167 and revised cooling circuits in the W222-and from 2019 the updated W213 facelift adopted the OM656.941 variant with CP4 fuel system revisions, creating interchange limits. All adaptations are documented in OEM technical bulletins.
Locate the engine code stamped horizontally on the front of the cylinder block near the timing cover (Mercedes-Benz TIS M12900). The 8th VIN digit indicates engine type ('6' for OM656 series). Pre-2019 models have silver valve covers with ribbed plastic covers; post-2019 units use black valve covers. Critical differentiation from OM656.941: Original .940 uses Bosch CP3 HPFP with circular fuel filter housing, while .941 uses CP4 with rectangular housing. Service parts require production date verification - fuel pumps and injectors before 06/2019 are not compatible with later units due to CP4 system integration (Mercedes-Benz SIB 20/2017).
The OM656.940's primary reliability risk is high-pressure fuel pump degradation, with elevated incidence in high-mileage and mixed-use conditions. Internal Mercedes quality reports from 2018 indicated a notable frequency of CP3 pump failures before 180,000 km in non-EU fuel markets, while UK DVSA data links EGR-related faults to urban-driven units. Extended idling and poor fuel quality increase HPFP and injector stress, making fuel filtration and oil interval adherence critical.
Analysis derived from Mercedes-Benz technical bulletins (2017-2022) and UK DVSA failure statistics (2018-2023). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about MERCEDES-BENZ OM656940.
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.
