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 pow…
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 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.
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.
The most common questions about engine codes, what they mean, how to find them and how this database works
The OM656.940 offers smooth performance and strong torque, but early models (2017-2018) are prone to HPFP failures, especially with poor fuel quality. Later revisions (post-2019) with CP4 pumps improved reliability. Well-maintained units with proper oil changes and quality diesel can exceed 250,000 km. Using MB 229.52 oil and adhering to service intervals is essential for longevity.
Key issues include high-pressure fuel pump failure, EGR valve and cooler clogging, turbo actuator sticking, and oil leaks from valve cover gaskets. These are documented in Mercedes-Benz service bulletins. Fuel quality significantly impacts HPFP and injector life. Regular EGR cleaning and use of OEM-spec oil help mitigate common failures.
This 3.0L inline-six diesel was used in the W213 E-Class (E350d), W222 S-Class (S350d), and W167 GLS-Class (GLS350d) from 2017 to 2023. It was phased out in favor of the OM656.942 in later model years. No cross-manufacturer usage is documented for this variant.
Yes, the OM656.940 responds well to ECU remapping. Stage 1 tunes typically add +40-60 kW safely, as the stock turbo and internals handle increased torque. Further gains require upgraded cooling, exhaust, and fuel system components. Tuning should be performed by specialists familiar with Bosch CRS 3.0 systems to avoid fuel pump strain.
In combined driving, the OM656.940 achieves approximately 7.0–7.8 L/100km (40–36 mpg UK). Highway driving can yield as low as 6.2 L/100km (~45 mpg UK), while city use may exceed 8.6 L/100km (~33 mpg UK). Real-world consumption depends on vehicle weight and driving style, but it remains competitive for a 3.0L diesel inline-six.
Yes. The OM656 series is an interference engine. If the timing chain fails or skips, pistons will contact open valves, resulting in catastrophic internal damage. While the front-mounted dual chain is robust, inspection beyond 200,000 km is advised. Any abnormal noise from the timing cover warrants immediate investigation.
Mercedes-Benz specifies SAE 0W-30 oil meeting MB 229.52 standard. This low-SAPS formulation is essential for DPF and turbo longevity. Oil changes should occur every 15,000 km or annually. Using non-compliant oil can lead to CCV clogging, increased oil consumption, and aftertreatment damage.
Comprehensive technical documentation and regulatory references
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MERCEDES-BENZ Official Site
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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
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