The Mercedes — Benz OM656.921 is a 2,925 cc, inline — six turbo — diesel engine produced between 2011 and 2018. It was developed as a refined, high — torque powerplant for executive and luxury SUV applications, featuring common — rail direct injection, variable geometry turbocharging (VGT), and double overhead camshafts (DOHC). In standard configuration, it delivered 150 kW (204 PS) and 500 Nm of torque, providing strong low — end pulling power with smooth delivery across…
Production years 2011–2018 meet Euro V emissions standards (VCA UK Type Approval #VCA/EMS/8903).
The Mercedes-Benz OM656.921 is a 2,925 cc inline-six turbo-diesel engineered for flagship sedans and large SUVs (2011–2018). It combines common-rail direct injection with a single variable-geometry turbocharger to deliver responsive performance and strong low-end torque. Designed to meet Euro V standards, it integrates SCR-AdBlue technology for NOx control while maintaining drivability in premium platforms.
| Parameter | Value | Source |
|---|---|---|
Displacement | 2,925 cc | |
Fuel type | Diesel | |
Configuration | Inline-6, DOHC, 24-valve | |
Aspiration | Turbocharged | |
Bore × stroke | 83.0 mm × 92.0 mm | |
Power output | 150 kW (204 PS) @ 3,800 rpm | |
Torque | 500 Nm @ 1,600–2,800 rpm | |
Fuel system | Bosch CRS 2.0 common-rail with piezoelectric injectors (up to 1,800 bar) | |
Emissions standard | Euro V | |
Compression ratio | 17.0:1 | |
Cooling system | Water-cooled | |
Turbocharger | Single variable-geometry turbo (Garrett GT1749V) | |
Timing system | Dual chain (front-mounted, long-life design) | |
Oil type | MB 229.51 (SAE 5W-30) | |
Dry weight | 210 kg |
The Mercedes-Benz OM656.921 was used across Mercedes-Benz's W212, W222, and X166 platforms with longitudinal mounting and designated for executive and luxury applications. This engine received platform-specific adaptations-higher-flow oil cooler in the GL 300 CDI BlueTEC and revised EGR calibration for stop-start duty-and from 2014 updated emissions control software to meet evolving Euro V requirements, creating minor service part and calibration differences. All adaptations are documented in OEM technical bulletins.
The OM656.921's primary reliability risk is piezoelectric injector degradation under sustained load, with elevated incidence in performance and urban applications. Internal Daimler reports from 2016 noted increased injector failure rates in pre-2014 units exceeding 180,000 km, while VCA MOT data links turbocharger performance faults to EGR clogging in city-driven GL-Class models. Extended idling and poor fuel quality amplify injector and turbo stress, making fuel filtration and oil change adherence critical.
Analysis derived from Mercedes-Benz technical bulletins (2011–2019) and UK DVSA failure statistics (2014–2021). 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 OM656.921 offers strong torque and smooth operation, but pre-2014 models are prone to piezoelectric injector issues under heavy use. Later revisions improved injector durability through better cooling and calibration. Well-maintained engines with regular oil changes and quality diesel can exceed 300,000 km. Using MB 229.51 oil and adhering to service intervals is essential for longevity.
Key issues include piezoelectric fuel injector failure, turbocharger actuator sticking, EGR/intake coking, and coolant leaks from the thermostat housing. These are documented in Daimler service bulletins and field reports. Fuel system health depends heavily on diesel quality and maintenance frequency, especially in performance and urban applications.
The OM656.921 was used in the W212 E-Class, W222 S-Class, and X166 GL-Class from 2011 to 2018. It was primarily offered as the E 300 CDI, S 300 CDI, and GL 300 CDI. All units meet Euro V standards and were built for executive and luxury applications.
Yes, but with caution. ECU remaps can safely increase output by +30–40 kW on stage 1, as the engine and turbo support moderate tuning. However, the piezoelectric injectors have limited headroom, and excessive tuning without upgraded fueling can lead to premature failure. Supporting mods like enhanced cooling and exhaust flow are recommended for sustained performance gains.
In the E 300 CDI, combined consumption is approximately 8.1–9.4 L/100 km (30–35 mpg UK), depending on load and driving style. Highway efficiency improves to ~6.8 L/100 km (41 mpg), while urban use can exceed 11 L/100 km (26 mpg). Real-world economy is highly dependent on vehicle weight and driving conditions.
Yes. The OM656.921 is an interference engine, meaning piston-to-valve contact occurs if timing is lost. While the front-mounted dual chain is robust, any sign of timing wear or noise must be investigated immediately to prevent catastrophic internal damage. Regular inspection per OEM intervals is strongly advised.
Mercedes-Benz specifies SAE 5W-30 oil meeting MB 229.51 standard. This low-ash formulation protects the fuel injectors and turbocharger, and must be changed every 15,000 km or annually. Using non-compliant oils increases the risk of injector wear and DPF clogging, especially under high-load operation.
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
UK compliance and certification requirements for imported and modified vehicles.
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