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 the rev range.
Fitted to the Mercedes-Benz E-Class (W212), S-Class (W222), and GL-Class (X166), the OM656.921 was engineered for drivers seeking a balance of refinement, efficiency, and towing capability. Emissions compliance was achieved through exhaust gas recirculation (EGR), a diesel particulate filter (DPF), and selective catalytic reduction (SCR) with AdBlue injection, enabling Euro V certification across its production run.
One documented concern is degradation of the piezoelectric fuel injectors under extended high-load operation, highlighted in Daimler Service Information Bulletin 27/2013. Internal coking and wear in the Bosch CRS 2.0 system can lead to misfires and uneven combustion. This issue was addressed through revised injector calibration and improved cooling strategies in post-2014 production units.
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 inline-six configuration delivers smooth, linear power ideal for spirited driving and towing but demands strict adherence to 15,000 km oil change intervals using MB 229.51 specification oil to protect the piezoelectric injectors and turbocharger. The Bosch CRS 2.0 system requires ultra-low-sulfur diesel (EN 590) to prevent coking and rail pressure instability. Turbo response is sharp at low RPM but sensitive to exhaust backpressure; blocked EGR passages can trigger DPF regeneration faults. Cooling system integrity is critical—overheating accelerates injector degradation. Post-2014 units benefit from revised fuel mapping and improved cooling per Daimler SIB 27/2013.
Oil Specs: Requires MB 229.51 (5W-30) specification (Mercedes-Benz SIB 27/2013). ACEA B5 or standard MB 229.5 insufficient.
Emissions: Euro V certification applies to all 2011–2018 models (VCA Type Approval #VCA/EMS/8903). No Euro IV or Euro VI variants produced.
Power Ratings: Measured under DIN 70020 standards. Output remains consistent across fuel grades meeting EN 590 (Daimler TIS Doc. A38640).
Mercedes-Benz Technical Information System (TIS): Docs A38202, A38640, SIB 27/2013
VCA Type Approval Database (VCA/EMS/8903)
SAE International: J1349 Engine Power Test Code
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.
Locate the engine code stamped horizontally on the front-left cylinder block near the timing cover (Mercedes-Benz TIS A38202). The 8th VIN digit indicates engine type ('M' for OM656 series). Pre-2014 models have silver valve covers with black intake manifolds; post-2014 units feature revised emissions control modules and updated ECU firmware. Critical differentiation from OM651.961: OM656.921 has inline-six layout, higher displacement, and enhanced SCR-AdBlue integration. Service parts require build-date verification—injectors and ECUs before 06/2014 are incompatible with post-2014 emissions systems (Daimler SIB 27/2013).
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.
Find answers to most commonly asked questions about MERCEDES-BENZ OM656921.
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EU emissions and type-approval regulations (e.g., CELEX:32007R0715, CELEX:32017R1151).
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DVLA: Engine Changes & MoT
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Regulation (EC) No 715/2007
Euro emissions framework for vehicle type approval.
Commission Regulation (EU) 2017/1151
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